Foam insulation made with expandable microspheres and methods

ABSTRACT

A polyurethane and/or polyisocyanurate foam is made using expandable microspheres which encapsulate a primary blowing agent. By expanding during the foam making process, the microspheres function as a blowing agent. The foam preferably has at least 10% by weight expandable micro spheres which encapsulate a non-halogenated hydrocarbon chemical or a non-halogenated hydrocarbon chemical blend and less than 2% by weight of any non-encapsulated blowing agents.

This application claims priority from U.S. Provisional Application No.60/293,793, filed May 25, 2001 and U.S. Provisional Application No.60/346,558, filed Jan. 8, 2002.

FIELD OF THE INVENTION

This invention relates to the manufacture of foam, particularly rigidpolyisocyanurate foam, wherein microspheres are expanded during the foammanufacturing process.

BACKGROUND

Hollow expandable microspheres containing volatile liquid blowing agentsencapsulated therein are beneficially employed as fillers in syntheticresinous castings, as bulking agents in textiles and paper, as thininsulating coatings, as blowing agent for other polymers, and the like.The synthesis of expandable particles is disclosed in a number ofpatents such as U.S. Pat. Nos. 3,615,972; 4,049,604; 4,016,110;4,582,756; 5,861,214; 5,155,138; EP 559,254; and PCT Publication No.WO/20465. These publications teach how to synthesize thermoplasticexpandable microspheres.

The shells of conventional thermoplastic microspheres are expanded byapplying heat, but become softened again and, then, easily broken, whenreheated. Conventional expanded thermoplastic polymer shells will alsobe easily broken when kept at high temperature for an extended amount oftime. These characteristics of prior art thermoplastic microspheressubstantially limit the applications of thermoexpandable microspheres inthe area where closed cell and high mechanical strength are required,such as in making polyurethane and polyisocyanurate rigid foams. Theinventors have recognized that it would be desirable to producethermoexpandable microspheres that can start expansion at a relativelylow temperature (e.g., 60° or 70° C.) and have a shell polymer of themicrospheres that becomes highly crosslinked at a higher temperature(e.g., 120° or 130° C.) when the microspheres are fully expanded. Thecrosslinking of the shell polymer is inactive at the onset of theexpansion temperature and will be activated at a higher temperature whenthe microspheres are fully expanded and, then, thermoset the shell ofthe expended microspheres.

In order to create such desirable microspheres, the inventors haverecognized several problems in the conventional manufacture ofmicrospheres themselves.

If the aqueous phase in a hypothetical process used to prepare polymermicrospheres is considered, the process looks like a suspensionpolymerization process, i.e. a water phase will contain a stabilizer, noinitiator is present, and an inhibitor is added to the aqueous phase inorder to prevent homogenous nucleation from occurring in the waterphase, resulting in a broadening of the particle size distribution. Theinventors have recognized that stabilization of the growing polymermicrospheres can be achieved by the addition of colloidal silica. Thecolloidal silica stabilizer is just one of several components that areneeded to be located at the water/oil interface. A polyester (preparedfrom a combination of diethanol amine and adipic acid in equimolarproportions) is often recommended as a co-stabilizer when usingcolloidal silica such as taught by U.S. Pat. Nos. 3,615,972; 4,582,756;and 5,834,526. However, substantial difficulties have been encounteredin maintaining the desired quality control of the amine/acid polyesteras reported in U.S. Pat. No. 4,016,110. Variation in the properties ofthe polyester result in batch-to-batch variation of the expandablemicrospheres prepared using the polyester. For conventional polyester, apH less than 7 has been recommended to impart good stability to thecolloidal silica which exhibited behavior similar to a polyelectrolyte,a polycation in this case. The behavior of the polyelectrolyte at anoppositely charged interface depends on the concentration of the polymeradded to the system. At low polyelectrolyte concentrations, bridgingoccurs between particles, and agglomeration of the colloidal silicaparticles takes place. The configuration of the polyelectrolyte in theadsorbed layer is dramatically affected by the presence of electrolytesin the aqueous phase. Significant flocculation will be obtained withpolyelectrolytes of high molar mass at low polyelectrolyteconcentration. Thus, the inventors recognize the molecular weight of thepolyelectrolyte and the stability of the molecular weight during thepolymerization process are very important. However, a polyesterstructure in the backbone is very sensitive to hydrolysis due to the lowpH, high temperature, and the amount of water. Thus, it would bedesirable if there were available an improved co-stabilizer whencolloidal silica is used in the preparation of polymer microspheres.

The removal of stabilizer used in the preparation of microspheres areusually difficult as described in U.S. Pat. Nos. 5,155,138 and5,834,526. The remaining colloidal silica on the microspheres afterpolymerization can influence the removal of water and the expansion ofthe microspheres. Co-stabilizer plays an important role in the washingoff of the colloidal silica stabilizer. As recognized by the inventors,some applications require that the microspheres contain very low watercontent. Thus, the inventors have recognized the desirability of using aco-stabilizer that can make it easy to wash off thestabilizer/co-stabilizer after polymerization of the polymer particles,resulting in a more simple process and lower water content in theresulting microspheres.

In one application, the microspheres are used in the manufacture ofsynthetic foam. Foams and processes for their production are well knownin the art. Such foams are typically produced by reacting ingredientssuch as a polyisocyanate with an isocyanate reactive material such as apolyol in the presence of a blowing agent.

Synthetic foams have many uses and are produced in many forms. Rigidfoam insulation panels are used in the construction of buildings. Foambun stock is used for freezer insulation. Flexible foam is used in themanufacture of automobiles and furniture. Shaped foam products are usedfor building facades and ornamental effects for both interior andexterior uses.

Foam products are generally highly flammable when made solely out oftheir basic components. A variety of materials have been used in thepast for imparting fire resistance to foams. For example, standardliquid flame retardants such as TRIS (-chloro-2-propyl) phosphateproducts, commercially available as ANTI-BLAZE 80 from Albright andWilson and as PCF from Akzo Nobel have been conventionally used toincrease the fire resistance of the foam. Such additives can be used toproduce Factory Mutual Class 1 rated foam when organic halogenatedhydrocarbons, such as 1,1-dichloro-1-fluorethane (HCFC-141b) are used asthe primary blowing agent.

Since the use of certain halogenated hydrocarbons may have detrimentalenvironmental effects, it is also desirable to provide foam made with anon-halogenated hydrocarbon as the primary blowing agent. However,similar foams made with non-halogenated hydrocarbons, such asiso-pentane and/or cyclopentane, used as the primary blowing agent failto produce Factory Mutual Class 1 rated foam. In such cases, the use ofexpandable graphite as a fire retardant 01/72863 A1.

Manufacturing foam with a non-halogenated hydrocarbon, such asiso-pentane, as the primary blowing agent conventionally requiresexpensive safety measures to be taken to avoid the fire and explainhazzard inherent with storing such blowing agents. Applicants haverecognized that the benefits of using non-halogenated hydrocarbons inthe manufacture of foam can be realized without the conventional safetyhazzards through the uses of the inventive microspheres whichencapsulates that highly flammable material.

SUMMARY

A polyurethane and/or polyisocyanurate foam is made using expandablemicrospheres which encapsulate a primary blowing agent. By expandingduring the foam making process, the microspheres function as a blowingagent. The foam preferably has at least 10% by weight expandablemicrospheres which encapsulate a non-halogenated hydrocarbon chemical ora non-halogenated hydrocarbon chemical blend and less than 2% by weightof any non-encapsulated blowing agents.

Preferably, two different average sizes of microspheres are used whenmaking boardstock or bunstock foam to enhance structural rigidity andstrength. Preferably, at least 30% of the microspheres have a relativelysmall average unexpanded diameter with a standard deviation less than 3microns and at least 30% of the microspheres have a relatively largeaverage unexpanded diameter with a standard deviation less than 9microns. The unexpanded diameter of the larger microspheres ispreferably at between 10 and 200 microns least and is 1.5 times greaterthan the unexpanded diameter of the smaller microspheres. The foam mayhave at least 45% of the microspheres having the smaller averageunexpanded diameter with a standard deviation less than 2 microns and atleast 45% of the microspheres having the larger average unexpandeddiameter with a standard deviation less than 8 microns where the largerdiameter is between 10 and 100 microns and is at least two times greaterthan the smaller diameter.

For best results, the foam is produced through mixing the constituentmaterials, including the expandable microspheres using a screw extruder.Alternatively, conventional mixing can be used for the foammanufacturing process.

Preferably, hollow thermoexpandable particles or microspheres areprovided that contain hydrocarbon blowing agents and have a shellpolymer that can be softened at the onset of the expansion temperatureand solidified at a higher temperature (thermoset) in an expanded state.Such a particle is advantageous for use in foam applications where closecell and mechanical strength of the foams are important.

Preferably, the thermoexpandable, thermoset hollow particles have agenerally spherical shape and are between 0.1 to 150 micrometers insize. The shell polymer preferably contains 0.5 to 20 wt % of thermallycrosslinkable monomer units based on the polymer weight. The volume ofthe hollow portion is preferably 5 to 50% of the total volume; and hasencapsulated within the hollow portion about 5 to 70 wt %, based ontotal weight of particle of hydrocarbon, fluid of between 3 and 7carbons which has a boiling point between about −60° C. and 70° C. Thefluid's boiling point is below the melting point of the non-thermosetshell polymer.

It has been discovered that high extent of encapsulation of blowingagents, symmetrical single droplet encapsulation, and low extent ofpremature crosslinking can be achieved when synthesizing the particlesusing two level polymerization temperatures (low and high temperaturepolymerization process).

The inventive microspheres are advantageously used to make foam. Theencapsulated blowing agent provides a relatively safe delivery of thisvolatile material to the foam making process while providing structuralbenefits.

By adjusting surface characteristics, the polymeric shell of theinventive microspheres become anchored in the foam through networkcrosslinking before expansion of the microspheres. This enhancesstructural stability of the rigid foam. While colloidal silica is apreferred stabilizer used in making the polymeric microspheres, silicaon the microsphere shell can inhibit the network crosslinking of themicrospheres within the foam. Thus, the use of a hydrogen peroxidetreatment on the microspheres, such as disclosed in U.S. Pat. No.4,179,546, aids in silica removal which in turn promotes microspherenetwork crosslinking with the foam in the foam manufacturing process.

It is an object of the invention to provide various methods for makingfoams including the use of an extruder and the use of microspheres whichencapsulate non-halogenated hydrocarbon agents to reduce the degree ofhazardous manufacturing conditions.

Other objects and advantages of the present invention will becomeapparent through a description of the presently preferred embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph illustrating the effect of the amount of ethanol andPVAm amount on microsphere size.

FIG. 2 is a contour plot showing the particle size with respect to theamount of PVAm and ethanol.

FIG. 3 is a contour plot showing the expanded volume of 0.2 gmicrosphere powder measured at 80° C.

FIG. 4 is a photograph of Example 54 microspheres from CM01 samplebefore expansion.

FIG. 5 is a photograph of Example 54 microspheres from CM01 sample afterexpansion.

FIG. 6 is a photograph of Example 57 microspheres from CM04 samplebefore expansion.

FIG. 7 is a photograph of Example 57 microspheres from CM04 sample afterexpansion.

FIG. 8 is a photograph of Example 68 microspheres from CM15 samplebefore expansion.

FIG. 9 is a photograph of Example 68 microspheres from CM15 sample afterexpansion.

FIG. 10 is a schematic illustration of an apparatus for extrudingpolymer foam, or dispersions for use in making such foam, in accordancewith the teachings of the present invention.

FIG. 11 is a cross-sectional side view of the extruder head of theextruder of FIG. 10.

FIG. 12 is a table of preferred boardstock formulations.

FIG. 13 is a table of preferred bunstock formulations.

FIG. 14 is a table of a preferred aqueous phase formulation used forExamples 70–71.

FIG. 15 is a table of a preferred oil phase formulation used for Example70.

FIG. 16 is a table of a preferred oil phase formulation used for Example71.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Expandable microspheres have an expandable polymer shell encapsulatingtherein a droplet of a liquid expanding agent such as a low boilinghydrocarbon or other volatile material that is generally a nonsolventfor the polymer. On heating the expandable microspheres to a temperaturesufficient to cause heat plastification of the shell, the microspheresexpand to form a hollow gas or vapor filled polymeric shell severaltimes the diameter of the unexpanded microspheres.

The shell polymer may contain heat activatible crosslinking agents thatremain inert at a temperature lower than the crosslinking temperature,which is higher than the softening temperature of the shell polymer. Thesoftening temperature is equatable to the glass transition temperatureof the expandable microsphere shell.

When temperature reaches the onset point of the heat activatingcrosslinking or above, the heat activatible crosslinking agentscrosslink, resulting in solidification of the shell polymer at hightemperature (higher than the expansion temperature). The special shellpolymer make the invented microspheres possess special expansionbehavior: they expand in a manor that is similar to that of conventionalthermoplastic microspheres when they are exposed at a temperature higherthan the softening point of the shell polymer and lower than the onsetof the heat activating crosslinking; their shell polymer expands and atthe same time crosslinks when they are exposed at a temperature higherthan the onset of the heat activating crosslinking; they expand tomaximum expansion ratio and then the shell polymer solidifies,maintaining the expanded volume of the microspheres when they are firstexposed at a temperature higher than the softening point of the shellpolymer and then exposed at a temperature higher than the onset of theheat activating crosslinking when the microspheres are fully expanded.As produced, the unexpanded particles are preferably spherical. Duringexpansion, the spherical shape is substantially maintained if theencapsulation of the volatile liquid is symmetrical and the polymershell is homogeneous in composition.

The heat activatible crosslinking agents, when used, are preferablyorganic compounds containing one kind of polymerizable unsaturateddouble bonds and one kind of functional groups, such as N-methylolacrylamide, -(isobutoxymethyl) acrylamide, methylolmethacrylamide,isobutoxymethylacrylamide, glycidol methacrylate, glycidyl methacrylate,glycidyl acrylate, dimethylaminoethyl methacrylate, acetoacetoxyethylmethacrylate, and the like. These functional groups become pendent oneson the shell polymer backbones when unsaturated double bonds havepolymerized and the shell of the microspheres have formed. These pendentfunctional groups are inert at low temperature and can react with eachother at elevated temperature when the microspheres fully expand to formcrosslinked network and thermoset the expanded microspheres.

The unexpanded microspheres generally have a number average diameter ofbetween about 1 and 200 microns, preferably 1 to 100 microns, and mostpreferable 1–50 microns. The particle sizes, and the size distributionsare measured by Horiba LA-910 Laser Scattering Particle SizeDistribution Analyzer, which is able to measure a wide range of particlediameters from very small (<1.0 micron) up to large particles (1,000microns).

The volatile hydrocarbon liquid will be retained in the hollow portionjust after expansion. Upon becoming rigid by crosslinking or cooling,the microspheres of the present invention become impermeable to gasexchange and retain their impermeability characteristics during aging.This is advantageous in reducing hazardous conditions in the manufactureof foam, since storage and processing foam using highlyflammable/explosive hydrocarbon materials, such as iso pentane, as aseparate component can be greatly reduce or eliminated.

The preferred expandable thermoset polymer that is used in making theinventive microspheres is an organic polymer made from copolymerizationof bi- or multi-functional monomers such as n-methylol acrylamide,glycidol methacrylate, n-isobutoxylmethyl acrylamide, dimethylaminoethylmethacrylate, and the like, preferably n-methylol acrylamide with one ortwo monofunctional monomers selected from:

-   (1) nitrile containing compounds such as acrylonitrile,    methacrylonitrile, and the like,-   (2) alkenyl aromatic compounds such as styrene, omethylstyrene,    m-methylstyrene, p-methylstyrene, ethylstyrene, vinyl-xylene,    chlorostyrene, bromostyrene, and the like,-   (3) acrylate or methacrylate containing compounds, such as alkyl    acrylates, alkyl methacrylates, wherein the alkyl group has carbon    number from 1 to 25, aromatic acrylates, aromatic methacrylates,    di-acrylate, di-methacrylate, poly-acrylates and polymethacrylates    monomers, and many other functionality containing compounds like    isobomyl acrylate or methacrylate, or some oligometric acrylate or    methacrylate compounds,-   (4) vinyl alkyl ester compounds, such as vinyl acetate, wherein the    alkyl groups is from carbon number 1 to 25,-   (5) vinyl alkyl ether compounds, such as butyl vinyl ethyl, wherein    the alkyl group is from carbon number 1 to 25;-   (6) halogenated monomers such as vinyl chloride, vinylidene    chloride, vinyl bromide, and the like.

The glass transition temperature (Tg) of the shell copolymer before itsheat activated crosslinking can be adjusted by the copolymer composition(the ratio of high Tg and low Tg components) to prepare the copolymershell with specific softening point before heat activated crosslinking.

A small amount of a normal crosslinking agent (different from the heatactivatible crosslinking agent) is preferably used to provide slightlycrosslinked shell polymer. This provides the polymer microspheres with arubbery plateau region. The rubbery plateau region can be extended torelatively higher temperature to increase the melting point withoutmodifying its initial onset point of glass transition by using theaforementioned normal crosslinking agent. Preferred normal crosslinkingagents are organic compound with two unsaturated double bonds such astriallyl cyanurate, hexamethylene dimethacrylate, ethylene glycoldimethacrylate, trimethylolpropane triacrylate, allyl methacrylate, andthe like, preferably triallyl cyanurate

The glass transition temperature and the melting point of the copolymershell is determined using differential scanning calorimetry (DSC).

The encapsulated volatile liquid can be an organic compound or themixture of several organic compounds of between 3 and 7 carbon atomsthat have a normal boiling point between −60° C. and 70° C., such asbutane, pentane, hexane, heptane, isobutene, isopentane, neopentane,cyclopropane, cyclobutane, cyclopropane, and the like, preferablyisopentane. The blowing hydrocarbon is chosen so that it is gaseous at atemperature below the glass transition temperature of the thermoplasticcopolymer.

The free radical polymerization initiator of the invention can be anyorganic compound that is capable of generating free radicals at certaintemperature range. Typical examples include organic peroxides and azoinitiators such as azobiscompounds.

Microspheres without Heat Activating Crosslinking Agent

To prepare the low temperature expandable microspheres of the inventionwithout a heat activated crosslinking agent, an oil mixture is preparedcontaining the monomers from which the thermoplastic is made, thevolatile organic liquid, the cross-linking agent, and a free radicalpolymerization initiator. Generally, the amounts of ingredients in thisoil mixture will be 50 to 95% by weight of the monomer, 5 to 50% byweight of the volatile organic liquid, 0 to 0.5% by weight of thecross-linking agent, and 0.1 to 3% by weight of the free radicalpolymerization initiator.

An aqueous phase is prepared by mixing water, a stabilizer of colloidalparticle dispersion, such as a fumed silica or silica gel or otherinorganic colloidal particles, a co-stabilizer such as poly(vinyl amine)with different molecular weight between 500 and 250,000 g/mol,preferably 25,000 g/mol, and an aqueous soluble free radical inhibitorsuch as sodium or potassium dichoromate. The pH of the aqueous mixtureis adjusted between 3 and 4, preferably 3.5 by using an acid, such ashydrochloric acid, acetic acid, hydronitric acid, and the like. Thecomposition of the aqueous phase affects the size of the oil dropletswhen the oil phase and aqueous phase are mixed. The term “oil” is usedherein as generic to liquids that are insoluble in water.

The two liquid mixtures are mixed by strong mechanical shear force andthe mixture is allowed to coalesce. The oil and aqueous phases are mixedin a ratio of between 1:25 to 2:1 oil mixture to aqueous mixture.Depending on the ratio and the composition of the oil and aqueousmixtures, the size of the droplets of polymerizable oil liquid can becontrolled. The size of these droplets, together with polymerizationconditions, will determine the size of the beads of the unexpandedmicrospheres.

The solid colloidal particles that are used in the aqueous mixture mustbe insoluble but dispersible in water and both insoluble andnondispersible in, but wettable by, the polymerizable liquid. The solidcolloids must be much more hydrophilic than eleophilic so as to remaindispersed wholly within the aqueous liquid. The solid colloids preferredin this invention are ones having particles that, in the aqueous liquid,retain a relatively rigid and discrete shape and size within the limitsstated. The particles may be greatly swollen and extensively hydrated,provided that the swollen particle retains a definite shape, in whichcase the effective size is approximately that of the swollen particle.The particles can be essentially single molecules, as in the case ofextremely high molecular weight cross-linked resins, or can beaggregates of many molecules. Materials that disperse in water to formtrue or colloidal solutions in which the particles have a size below therange stated or in which the particles are so diffuse as to lack adiscernible shape and dimension are not suitable as stabilizers forlimited coalescence. The amount of solid colloid that is employed isusually such as corresponds to from about 0.01 to about 10 or more gramsper 100 cubic centimeters of the polymerizable liquid.

In order to function as a stabilizer for the polymerizable droplets, itis important that the solid colloid tends to collect within the aqueousliquid at the liquid-liquid interface, i.e. on the surface of the oildroplets. In many instances, it is desirable to add a “co-stabilizer”material to the aqueous composition to drive the particles of the solidcolloid to the liquid-liquid interface. Usually, the co-stabilizers areorganic materials that have affinity for the solid colloid and also forthe oil droplets and that are capable of making the solid colloid moreeleophilic. The affinity for the oil surface is usually due to someorganic portion of the co-stabilizer molecule while the affinity for thesolid colloid is usually due to opposite changes. For example,negatively charged colloids, such as bentonite, are promoted bypositively charged co-stabilizers such as tetramethyl ammonium hydroxideor chloride or water-soluble complex resinous amine condensationproducts such as the water-soluble condensation products ofdiethanolamine and adipic acid, the water-soluble condensation productsof ethylene oxide, urea and formaldehyde, and polyethylenimine.

Usually, the co-stabilizer is used only to the extent of a few parts permillion of aqueous medium, although larger proportions can often betolerated. Although the percentage of the co-stabilizer to be used isvery little, it imparts a significant influence in the synthesis of theexpandable microspheres, such as in the extent of the encapsulation ofthe blowing agent, reproducibility of the synthesis, removal of thecolloidal particles after polymerization, and in the drying process.U.S. Pat. No. 4,798,691 reported a good polyester co-stabilizer which isthe condensation product of diethanol amine and adipic acid. However,this co-stabilizer has many drawbacks. For example, this co-stabilizeris easy to be hydrolyzed when dissolved in water, especially under theconditions of low pH and high temperature. The hydrolysis will changethe molecular weight of the polyester co-stabilizer, resulting in poorreproducibility in the synthesis of microspheres using polyesterco-stabilizer.

Poly(vinyl amine) co-stabilizer with different molecular weightdeveloped by this invention has proved to be a better co-stabilizer. Itprovides very good reproducibility of the synthesis of expandablemicrospheres. It has better promotion ability to drive the colloidalsilica to the liquid-liquid interface which improves the stability ofthe system and the encapsulation. Poly(vinyl amine) co-stabilizer canalso be easily removed when the polymerization ends, which makes thesubsequent drying process simple since it can be air-dried. This resultsin very low water content in the final microsphere products. Thepoly(vinyl amine) used in this invention is preferably of molecularweight between 500 g/mol to 250,000 g/mol, preferably 25,000 g/mol.

The oil droplets dispersed in the aqueous medium are polymerized in apressure reactor under an agitation that allows proper heat transferbetween the mixture and the reactor. Polymerization temperaturesubstantially influence the quality of the resulting expandablemicrospheres. The polymerization temperature preferably ranges from 5°to 150° C. for 0.1 to 48 hours.

The load of the reactor will influence the synthesis, too. The higherthe initial pressure caused by some inert gases such as nitrogen, argon,and the like, the larger extent of the encapsulation of the volatileorganic liquid. In the case that the volatile monomers are used such asvinylidene chloride and the like, the initial pressure provided by aninert gas will reduce the amount of the volatile monomer in the gaseousspace of the reactor, which will remain the composition of the oildroplets. The initial pressure used in this invention is preferablybetween 0 to 500 atmospheres, which can be selected based on thepolymerization temperature.

The particles can be removed from the reaction mixture by filtration, bysedimentation, or by coagulation using a solvent, such as an alcohol;washed with water and dried. If the product is to isolated as unexpandedmicrospheres, it can be dried at or below the temperature that at least5° C. below the glass transition temperature of the shell copolymerusing air flow.

The low temperature expandable thermoplastic microspheres are useful ininsulation, packaging, for making foam materials such as polyurethane orpolyisocyanurate rigid foams. In particular, making such foams using themethods set forth in U.S. Pat. No. 5,723,506 (Glorioso et al. ), wherethe microspheres of the present application are used as filler materialwhile also serving to deliver the blowing agent.

EXAMPLE 1

An oil phase was prepared using 69.6 parts of vinylidene chloride, 14.4parts of acrylonitrile, 4.2 parts of methyl acrylate, 0.2 parts oftriallyl cyanurate, 21.6 parts of iso-pentane, and 0.84 parts of2,2′-azobis(isobutyronitrile). Separately, an aqueous phase mixture wasprepared utilizing 120 parts of deionized water, 18 parts of colloidalsilica dispersion (30 weight percent solid available under the tradename of “Ludox HS-30”), 0.84 parts of a solution containing 8.2 weightpercent of poly(vinyl amine) of 25,000 g/mol molecular weight, and 2.04parts of a solution containing 2.5 weight percent sodium dichromate. ThepH value of the aqueous phase mixture was adjusted between 3 and 4,preferable 3.5 with hydrochloric acid. After the oil and aqueous phaseswere mixed, the mixture was violently mixed by a homogenizer, OMNI PRO300 type, available from PRO Scientific Inc. Preferably mixing is at aspeed between 6000 and 8000 rpm for 3 to 15 minutes in an ice water bathat temperature between 2° and 5° C. The resultant mixture wasimmediately transferred to a pressure reactor and sealed. The reactionmixture was maintained at a temperature of 60° C. for 16 hours undermild rotation of 40 rpm. The reactor was filled to a level of 90%. Theobtained produce was filtrated, washed, and dried at room temperature.The unexpanded microspheres obtained had average particle size between 5and 50 microns determined by Horiba LA-910 Laser Scattering ParticleSize Distribution Analyzer (which is the method for determination ofparticles size in all examples), and gave the maximum volumetricexpansion ratio of about 70 times when samples are placed in a thin andlong glass tube, uniform in certain diameter, heated in water bath at atemperature of 80° C. The volume expansion ratio is determined bymarking the height of total unexpanded microspheres residing inside thethin glass tube and the height of the expanded microspheres inside thetube. Assuming uniformity in glass tube diameter, initial volume beforethermal expansion and final volume after thermal expansion can bedetermined. The volume expansion ratio is essentially the height ratioif the diameter of the glass tubing remains constant, which is the casefor all examples hereafter. When observed under the optical microscopeequipped with a heating stage that can control the heating rate, themicrospheres synthesized above started expansion at a temperaturebetween 65° and 70° C. and can sustain at a temperature up to 120° C.when heating rate is 6° C./min. In Examples 1–9, the temperature wherethe microspheres start to expand and the highest temperature that theexpanded microspheres can still sustain are all measured by the methoddescribed above. The air-dried microspheres had a water content of about0.5 weight percent. The water content was measured by monitoring theweight loss when the air-dried microspheres were further dried in vacuumover for 72 hours, which is the case for all Examples 1–9.

EXAMPLE 2

The procedure of Example 1 was repeated with the exception that there isno triallyl cyanurate in the oil mixture. The obtained microspheres hadsimilar particles size and water content to those prepared in Example 1,and had a maximum volumetric expansion ratio of about 52 times whenheated in water bath at a temperature of 80° C., and started expansionat a temperature about 65° C. and sustained at a temperature of 85° C.when heating rate is 6° C./min.

EXAMPLE 3

The procedure of Example 1 was repeated with the exception that 0.2parts of triallyl cyanurate was replaced by 0.14 parts of allylmethacrylate in the oil mixture. The obtained microspheres had similarparticles size and water content to those prepared in Example 1, and hada maximum volumetric expansion ratio of about 60 times when heated inwater bath at a temperature of 80° C.

EXAMPLE 4

The procedure of Example 1 was repeated with the exception that 0.2parts of triallyl cyanurate was replaced by 0.18 parts of ethyleneglycol dimethacrylate and 0.84 parts of 2,2′-azobis(isobutyronitrile)was replaced by 1.18 parts of 2,2′-azobis(isobutyronitrile). Theobtained microspheres had similar particles size and water content tothose prepared in Example 1, and had a maximum volumetric expansionratio of about 60 times when heated in water bath at a temperature of80° C.

EXAMPLE 5

The procedure of Example 1 was repeated with the exception that 0.2parts of triallyl cyanurate was replaced by 0.13 parts of hexamethylenedimethacrylate. The obtained microspheres had similar particles size andwater content to those prepared in Example 1, and had a maximumvolumetric expansion ratio of about 70 times when heated in water bathat a temperature of 80° C.

EXAMPLE 6

The procedure of Example 1 was repeated with the exception that 0.2parts of triallyl cyanurate was replaced by 0.12 parts oftrimethylolpropane triacrylate. The obtained microspheres had similarparticles size and water content to those prepared in Example 1, and hada maximum volumetric expansion ration of about 45 times when heated inwater bath at a temperature of 80° C.

EXAMPLE 7

The procedure of Example 1 was repeated with the exception that 0.84parts of 2,2′-azobis(isobutyronitrile) was replaced by 1.8 parts oft-amyl peroxyneodecanoate (75 weight percent solid dissolved in mineraloil available under the trade name of “Lupersol 54B M75”), and thepolymerization was performed in Example 1, had particle size between 1and 40 microns, and had a maximum volumetric expansion ratio of about 80times when heated in water bath at a temperature of 80° C.

EXAMPLE 8

The procedure of Example 7 was repeated with the exception that aninitial pressure of 3 atmospheres was applied using nitrogen gas beforethe polymerization started. The obtained microspheres had similarparticles size and water content to those prepared in Example 7, and hada maximum volumetric expansion ratio of about 90 times when heated inwater bath at a temperature of 80° C.

EXAMPLE 9

The procedure of Example 1 was repeated with the exception that (69.6parts of vinylidene chloride, 14.4 parts of acrylonitrile, 4.2 parts ofmethyl acrylate) was replaced by (72 parts of vinylidene chloride and 12parts of acrylonitrile). The obtained microspheres had similar particlessize and water content to those prepared in Example 1, and had a maximumvolumetric expansion ratio of about 46 times when heated in water bathat a temperature of 80° C.

Microspheres with Heat Activated Crosslinking Agent

To prepare the thermoexpandable thermoset microspheres of the inventionwith a heat activated crosslinking agent, an oil mixture is preparedcontaining the monomers from which the shell polymer is made, thehydrocarbon liquid, the normal crosslinking agent, the heat activatiblecrosslinking agent, and a free radical polymerization initiator.Generally, the amounts of ingredients in this oil mixture will be 50 to95% by weight of the monomer, 5 to 50% by weight of the volatilehydrocarbon liquid, 0 to 0.5% by weight of the normal crosslinkingagent, 1 to 10% by weight of the heat activatible crosslinking agent,and 0.1 to 3% by weight of the free radical polymerization initiator.

An aqueous phase is prepared by mixing water, a stabilizer of colloidalparticle dispersion, such as a fumed silica or silica gel or otherinorganic colloidal particles, a costabilizer such as poly(vinyl amine)with molecular weight between 500 and 250,000 g/mol, and an aqueoussoluble free radical inhibitor such as sodium or potassium dichromate.The pH of the aqueous mixture is adjusted between 3 and 4, preferably3.5 by using an acid, such as hydrochloric acid, acetic acid,hydronitric acid, and the like, preferably hydrochloric acid. Thecomposition of the aqueous phase affects the size of the oil dropletswhen the oil phase and aqueous phase are mixed. The term “oil” is usedherein as generic to liquids that are insoluble in water.

The two liquid mixtures are mixed by strong mechanical shear force andthe mixture is allowed to coalesce. The oil and aqueous phases are mixedin a ratio of between 1:25 to 2:1 oil mixture to aqueous mixture.Depending on the ratio and the composition of the oil and aqueousmixtures, the size of the droplets of polymerizable oil liquid can becontrolled. The size of these droplets, together with polymerizationconditions, will determine the size of the beads of the unexpandedmicrospheres.

The preferred solid colloidal particles, a stabilizer, and co-stabilizerfor the microspheres remain the same for microspheres having a heatactivated crosslinking agent as explained above for microspheres withoutsuch agent.

Oil droplets are dispersed in an aqueous medium and are polymerized in apressure reactor under an agitation that allows proper heat transferbetween the mixture and the reactor. Polymerization temperaturesubstantially influence the quality of the resulting expandablemicrospheres. Low temperature favors the encapsulation of volatilehydrocarbon liquid, the stability of the suspension system, and theprotection of the heat activatible crosslinking groups, but decreasesthe uniformity of the composition of the shell copolymer. Hightemperature has the opposite effects. A process that polymerizes the oildroplets initially at a lower temperature and then elevates thetemperature to a higher level was developed using a combination ofinitiators with different half-lives to produce the microspheres ofExamples 15–17, below. The polymerization temperature preferably rangesfrom 5 to 150° C. for 0.1 to 48 hours.

The load of the reactor will also influence microsphere synthesis. Thehigher the initial pressure caused by some inert gases such as nitrogen,argon, and the like, the larger extent of the encapsulation of thehydrocarbon liquid. Where volatile monomers are used, such as vinylidenechloride and the like, the initial pressure provided by an inert gaswill reduce the amount of the volatile monomer in the gaseous space ofthe reactor, which will maintain the composition of the oil droplets.The initial pressure is preferably between 0 to 500 atmospheres and canbe selected based on the polymerization temperature. The pressure ispreferably high enough to maintain the blowing agent in a liquid form atthe polymerization temperature.

The particles can be removed from the reaction mixture by filtration, bysedimentation, or by coagulation using a solvent, such as an alcohol;washed with water and dried. If the particles are to be isolated asunexpanded microspheres, they are preferably dried using air flow at orbelow a temperature that is at least 5° C. below the glass transitiontemperature of the shell copolymer before its heat activatedcrosslinking.

Thermoexpandable thermoset microspheres have a variety of uses,particularly in insulation, packaging, and for making foam materialssuch as polyurethane or polyisocyanurate rigid foams. For use in foammanufacture, the microspheres are preferably treated with hydrogenperoxide, such as disclosed in U.S. Pat. No. 4,179,546. This treatmentassists in silica removal from the polymeric shells of the microsphereswhich in turn promotes network crosslinking in foam manufacture.

EXAMPLE 10

An oil phase was prepared using 835.2 parts of vinylidene chloride,172.8 parts of acrylonitrile, 120.0 parts of a water solution containing48 weight percent of N-methylol acrylamide, 3.6 parts of triallylcyanurate, 259.2 parts of iso-pentane, and 21.6 parts of t-amylperoxyneodecanoate (75 weight percent solid dissolved in mineral oilavailable under the trade name of “Lupersol”). Separately, an aqueousphase mixture was prepared utilizing 1440 parts of deionized water, 216parts of colloidal silica dispersion (30 weight percent solid availableunder the trade name of “Ludox HS-30”), 10.08 parts of a solutioncontaining 8.2 weight percent of poly(vinyl amine) of 25,000 g/molmolecular weight, and 24.48 parts of a solution containing 2.5 weightpercent sodium dichromate. The pH value of the aqueous phase mixture wasadjusted between 3 and 4, preferable 3.5 with hydrochloric acid. Afterthe oil and aqueous phases were mixed, the mixture was violently mixedby a homogenizer, OMNI PRO 300 type, available from PRO Scientific Inc.Preferably, mixing is at a speed between 6000 and 8000 rpm for 5 to 30minutes in an ice water bath at temperature between 2 and 5° C. Theresultant mixture was immediately transferred to a 3-liter pressurereactor with anchor impeller and sealed with no additional pressurebeing applied. The reaction mixture was maintained at a temperature of45° C. for 16 hours under mild agitation speed of 40 rpm to polymerizethe oil droplets. The reactor was filled to a level of 90%. The obtainedproduct was filtrated, washed, and dried at room temperature.

The unexpanded microspheres obtained had number average particles sizebetween 1 and 30 microns determined by Horiba LA-910 Laser ScatteringParticle Size Distribution Analyzer (which is the method fordetermination of particles size in all examples), and gave the maximumvolumetric expansion ratio of about 90 times when samples are placed ina thin and long glass tube, uniform in certain diameter, heated in waterbath at a temperature of 80° C. The retention of the expanded statereflects the occurrence of crosslinking and thermosetting of themicrosphere shells.

The volume expansion ratio is determined by marking the height of totalunexpanded microspheres residing inside the thin glass tube and theheight of the expanded microspheres inside the tube. Assuming uniformityin glass tube diameter, initial volume before thermal expansion andfinal volume after thermal expansion can be determined. The volumeexpansion ratio is essentially the height ratio if the diameter of theglass tubing remains constant, which is the case for all exampleshereafter.

When observed under the optical microscope equipped with a heating stagethat can control the heating rate, the microspheres synthesized abovestarted expansion at a temperature between 69 and 75° C. and can sustainat a temperature up to 140° C. when heating rate is 6° C./min. Theincrease in the maximum sustain temperature of the expanded microspheresindicates the heat activated crosslinking occurs. In all the exampleshereafter, the temperature where the microspheres start to expand andthe highest temperature that the expanded microspheres can still sustainare all measured by the method described above. The air-driedmicrospheres had a water content of about 0.6 weight percent. The watercontent was measured by monitoring the weight loss when the air-driedmicrospheres were further dried in vacuum oven for 72 hours, which isthe case for all examples hereafter.

EXAMPLE 11

The procedure of Example 10 was repeated with the exception that 120parts of a water solution containing 48 weight percent of N-methylolacrylamide was mixed in the aqueous phase instead of in the oil phase.Similar results as those in Example 10 were obtained.

EXAMPLE 12

The procedure of Example 10 was repeated with the exception that 120parts of was replaced by 60 parts of a solution containing 48 weightpercent of N-methylol acrylamide and 48.12 parts of methyl acrylate inoil mixture. The obtained microspheres had similar particles size andwater content to those prepared in Example 10, and had a maximumvolumetric expansion ratio of about 85 times when heated in water bathat a temperature of 80° C. When observed under the optical microscopeequipped with a heating stage that can control the heating rate, themicrospheres synthesized above started expansion at a temperature 75° C.and can sustain at a temperature up to 130° C. when heating rate is 6°C./min.

EXAMPLE 13

The procedure of Example 10 was repeated with the exception that 120parts of a water solution containing 48 weight percent of N-methylolacrylamide was replaced by 50 parts of glycidol methacrylate. Theobtained microspheres had similar particles size and water content tothose prepared in Example 10, and had a maximum volumetric expansionratio of about 70 times when heated in water bath at a temperature of80° C. When observed under the optical microscope equipped with aheating stage that can control the heating rate, the microspheressynthesized above started expansion at a temperature 72° C. and cansustain at a temperature up to 128° C. when heating rate is 6° C./min.

EXAMPLE 14

The procedure of Example 13 was repeated with the exception that 50parts of glycidol methacrylate was replaced by 50 parts ofN-isobutoxymethyl acrylamide. The obtained microspheres had similarparticles size, sustain temperature, and water content to those preparedin Example 13, and had a maximum volumetric expansion ratio of about 65times when heated in water bath at a temperature of 80° C.

EXAMPLE 15

The procedure of Example 10 was repeated with the exception that 21.6parts of t-amyl peroxyneodecanoate (75 weight percent solid dissolved inmineral oil available under the trade name of “Lupersol”) was replacedby (5.52 parts of 2,2′-azobis(siobutyronitrile) and 12.0 part of theLupersol), 120.0 parts of a water solution containing 48 weight percentof N-methylol acrylamide was replaced by 50 parts of methyl acrylate,and the oil droplets dispersed in the aqueous phase were firstpolymerized at a temperature of 45° C. for 12 hours and then furtherpolymerized at a temperature of 65° C. for another 8 hours. The obtainedmicrospheres had similar particles size and water content to thoseprepared in Example 10, and had a maximum volumetric expansion ratio ofabout 55 times when heated in water bath at a temperature of 80° C. Somesmall particles did not expand.

EXAMPLE 16

The procedure of Example 15 was repeated with the exception that ainitial pressure of 3 atmospheres was applied using nitrogen gas at theend of the first 12-hour polymerization. The obtained microspheres hadsimilar particles size and water content to those prepared in Example15, and had a maximum volumetric expansion ratio of about 76 times whenheated in water bath at a temperature of 80° C.

EXAMPLE 17

The procedure of Example 16 was repeated with the exception that 50parts of methyl acrylate was replaced by 120.0 parts of a water solutioncontaining 48 weight percent of N-methylol acrylamide. The obtainedmicrospheres had similar particles size and water content to thoseprepared in Example 10, and had a maximum volumetric expansion ratio ofabout 90 times when heated in water bath at a temperature of 80° C. Whenobserved under the optical microscope equipped with a heating stage thatcan control the heating rate, the microspheres synthesized above startedexpansion at a temperature 70° C. and can sustain at a temperature up to145° C. when heating rate is 6° C./min.

Control of Microsphere Size and Size Distribution

Experimentation showed that the composition of the aqueous phase wasfound to have great effect on the morphology and expansion properties ofthe microspheres. The amount and type of alcohol used in the suspensionpolymerization recipe had the most significant effect. Methanol, andethanol, in particular, result in an increase in the particle size andnarrow the particle size distribution. An optimum amount of methanol orethanol brings about a sharp expansion of the particles during heatingresulting from the uniformity of the particle properties. However, toomuch methanol or ethanol produces particles with a honeycomb structure,which do not maintain the particle integrity at higher temperatures andlead to a poorer expansion.

The use of butanol did not improve the thermal-expansion properties. Theuse of increasing amounts of poly(vinyl amine) (PVAm), which acted as asteric stabilizer together with the colloidal silica, producedmicrospheres that were smaller and more uniform in size. However, themolecular weight of the poly(vinyl amine) did not affect the particleproperties. The amount of Ludox® colloidal silica had little effect onthe particle size and size distribution, but it did affect the degree ofexpansion of the particles. Smaller amounts of Ludox® resulted in betterexpansion. The level of salt did not have any effect on the particlesize, but it appeared to broaden the particle size distribution andincrease the onset temperature of both expansion and shrinkage.

Higher agitation speeds in the preparation of the dispersion producedparticles with narrower size distributions. This may be attributed to anarrower initial droplet size distribution. The agitation time hadlittle effect on the particle size, but it appeared to narrow theparticle size distribution.

The presence of shear during an H₂O₂ post-surface treatment enhancesexpansion properties. Air-dried particles bring about better expansionafter H₂O₂ surface treatment compared to an original slurry directlytaken from reactor.

A systematic investigation of the effect of the amount of PVAm andethanol on the particle properties was carried out and an optimum regionwas found for producing particles with excellent expansion properties.

The microspheres were made using a suspension polymerization process. Inthe suspension polymerization process, the stabilized monomer dropletsare polymerized directly to form polymer particles; therefore, themonomer droplet can be viewed as a small bulk polymerization reactor.With the assumption that the polymerization is subject to a free-radicalmechanism, the bulk polymerization rate equation can be applied to asuspension polymerization system at low to moderate conversions:

$\begin{matrix}{R_{p} = {{k_{p}\lbrack M\rbrack}\left( \frac{2{{fk}_{d}\lbrack I\rbrack}}{k_{t}} \right)^{0.5}}} & {{Equation}\mspace{14mu}(1)}\end{matrix}$where R_(p) is the rate of polymerization.; [M] and [I] are the monomerand initiator concentrations, respectively; k_(p), k_(d) and k_(t), arethe rate constants for propagation, initiation and terminationrespectively; and f is the free-radical efficiency.

Suspension polymerization kinetics consists of three stages. In stage 1,the viscosity of the organic phase is low, the droplet size is small andthe particle size distribution (PSD) is narrow, depending on the amountof agitation and concentration of suspending agent. Also the suspensionis quite stable, the droplet population dynamics (break-up/coalescenceof droplets) are fast, and the quasi-steady state assumption is valid.In stage 2, which starts around 20–35% conversion, the droplets becomehighly viscous and viscoelastic, the breakage and coalescence ratesdecrease. The extent of droplet breakage slows down faster than thedroplet coalescence rate, and the average droplet size increases. Ifcoalescence dominates, or if stage 2 lasts too long, a broader PSD oreven agglomeration will occur. In stage 3, the conversions are evenhigher and the particles become solid. Monomer diffusion limitationsbecome evident and the propagation rate decreases.

Many parameters can influence the microsphere size, size distribution,and morphology. The initial droplet size and size distribution duringpreparation of the dispersion are crucial to the final particle size andsize distribution. When using comminution method to make an emulsion,assuming the absence of recoalescence of the droplets, the final averagedroplet size, d, is given by

$\begin{matrix}{d = \frac{6\varphi\; M_{s}\Gamma_{\max}}{W_{s}}} & {{Equation}\mspace{14mu}(2)}\end{matrix}$where: φ is the volume fraction of the oil phase, Ws is the mass of thestabilizer added per unit volume of emulsion, and Ms is the molecularweight of the stabilizer molecules. Γ_(max) is the monolayer volume ofthe adsorbed amount in the corresponding adsorption isotherm of thestabilizer at the oil/water interface.

The degree to which the polymer dissolves, swells, or precipitates inthe monomer phase, the presence of monomer diluents or cross-linkingmonomer, and the concentration and type of oil-soluble initiator can allgreatly influence the surface and bulk morphology of the productparticles.

Morehouse, Jr, D. S., in U.S. Pat. No. 3,615,972, describes a suspensionpolymerization process that was employed to produce expandablethermoplastic polymer particles containing a volatile fluid foamingagent. The polymerization began with an aqueous dispersion of: (1)organic monomers that were suitable for polymerization to form athermoplastic resinous polymer having the desired physical properties;(2) a liquid blowing agent which exerts little solvent action on theresulting polymer and in a quantity in excess of that which is solublein the polymer; (3) a dispersion stabilizing material which is utilizedto maintain the dispersion, subsequently polymerizing the monomericmaterial to solid spherical particles having the liquid-blowing agentencapsulated therein as a distinct and separate phase.

Various organic materials can be used as monomers in this process.Generally, they may be: (1) alkenyle aromatic monomers; (2) acrylatemonomers alone, or in combination with the alkenyl aromatic monomers;(3) halogenated vinyl compounds, e.g., vinylidene chloride,acrylonitrile with vinyl chloride; (4) esters, e.g., vinyl acetate,vinyl butyrate; and (5) copolymerizable acids, e.g., acrylic acid,methacrylic acid.

The blowing agents may fall into the following types of organicmaterials: (1) aliphatic hydrocarbons, e.g. ethane, ethylene, propane,isopentane; (2) chlorofluorocarbons, e.g. CCl₃F, CCl₂F₂, CCl F₃—CCl₂F₂;(3) tetraalkyl silanes, e.g. tetramethyl silane. The boiling point ofsuch blowing agents at atmospheric pressure should be about the sametemperature range or lower than the softening point of the resinousmaterial employed.

In the following Examples, an inorganic stabilizer, colloidal silica(Ludox® HS, Sigma-Aldrich), and water-soluble polymer, poly(vinyl amine)(PVAm, BASF) were used. PVAm was employed to further protect the monomerdroplets against coalescence by increasing the viscosity of the systemand acted as a bridge between silica colloidal particles and the monomerdroplets. Sometimes a small amount of electrolyte, e.g., water-solubleionizable alkali, acid or salt, is used to drive the solid colloids tothe oil-water interface; in the following Examples common salt (NaCl)was employed. Oil-soluble initiators such as benzyl peroxide, or azoinitiators such as 2,2′-azobis(isobutyronitrile) (AIBN) can be used; asnoted below AIBN was used in the following Examples. Since it isdesirable that the polymerization only takes place within the monomerdroplets, Na₂Cr₂O₇ was used to inhibit any aqueous phase polymerization.

In the monomeric phase, it is beneficial to add a difunctional monomeror cross-linking agent, such as TAC (triallyl cyanurate) to increase themelt or flow viscosity of the polymeric composition at temperatures highenough to cause volatilization of the blowing agent and subsequentdeformation of the originally formed sphere into a larger hollow sphereafter particle expansion. As noted below, TAC was used in the followingExamples.

Gamer, J. L., in U.S. Pat. 3,945,956, reported that the addition of analcohol to the polymerization system can result in the formation oflarger particles with narrower size distributions and improved expansioncharacteristics. Ejiri, M., in European Patent No. 1,054,034 A1,disclosed that the presence of at least one compound selected from thegroup consisting of alkali metal nitrites, stannous chloride, stannicchloride, water-soluble ascorbic acids and boric acid can produceexpandable microspheres with extremely sharp PSDs, and excellentexpansion properties.

EXAMPLES 18–69

Vinylidene chloride (VDC, Sigma-Aldrich), acrylonitrile (AN,Sigma-Aldrich) and methyl acrylate (MeA, Sigma-Aldrich) monomerstogether with triallyl cyanurate (TAC, Monomer-Polymer & Dajac Labs Inc.) and 2-methyl butane (iso-pentane, Sigma-Aldrich) were mixed with2,2′-azobis(isobutyronitrile) (AIBN, Sigma-Aldrich) to form the oilphase. Deionized (DI) water, colloidal silica (Ludox®, Sigma-Aldrich),NaCl (>99.9%, Fisher), Na₂Cr₂O₇ (Sigma-Aldrich), poly(vinyl amine)(PVAm, MW=15,000, 50,000, or 250,000 g/mol, from BASF), and alcohols(methanol, ethanol, n-propanol, -butanol and hexanol all fromSigma-Aldrich) comprise the aqueous phase. All of these chemicals areused as received.

Generally following the methods described in U.S. Pat. No. 3,945,956 andU.S. Pat. No. 3,615,972, the following standard recipe was used for thepreparation of microspheres and investigation of the effects ofdifferent variables in the following Examples.

TABLES 1 and 2 Standard Recipe for Examples 18–69 Aqueous Phase OilPhase Chemical Amount (g) Chemical Amount (g) Deionized water 200.0 VDC116.0 Ludox ® colloidal silica 30.0 AN 24.0 (35 wt %) NaCl 4.0 MeA 7.0Na₂Cr₂O₇(2.5 wt %) 3.4 AIBN 1.4 PVAm* 0.12 TAC 0.35 Alcohol 2.0Isopentane 36 *The amount of PVAm is for the solid polymers.

All of the organic components of the oil phase were weighted and mixedin advance, and stored chilled in ice before mixing with the aqueousphase. The aqueous phase was prepared by adding Ludox®, Na₂Cr₂O₇, andNaCl to DI water, and then carefully mixing in the PVAm. The pH of themixture was adjusted from about 7 to 3.5 by adding HCl. Then the twophases were mixed together in a 1L glass reactor (Lab Glass), andsimultaneously the alcohol was added into the mixture with mildagitation of the six-bladed steel propeller. To prevent monomer fromvaporizing, the reactor was kept cold by immersing it in ice throughoutthe preparation process. The mixture was agitated at a certain agitationspeed (i.e., from 1000 to 1960 rpm) for about 15–30 minutes until thetwo phases were totally emulsified. The resulting dispersion was thenput into a pressure bottle (250 mL, Lab Glass) for polymerization. Thereaction was carried out in a bottle polymerization unit (rotation speedis about 30 rpm) at 60° C. for about 20 hours in order to achieve highconversion. The resulting slurry was first filtered through a 280-meshscreen to remove any aggregated large beads, then collected on a filterpaper and dried in the air.

The produced polymer particles were not expandable unless they weretreated by hydrogen peroxide. To do this, 50 g of the microsphere slurry(40 wt % microspheres) was heated to 50° C. for 3.5 hour and treatedwith 0.4 g hydrogen peroxide solution. In the following Examples, mostsurface treatments were carried out in a bottle polymerization unit.Under a microscope, the shell of the treated microspheres wastransparent and was thermally expandable as compared to the untreatedparticles.

Static light scattering (Horiba, model LA-910) was used to measure theparticle size and size distribution. Deionized water was used as thedispersion medium. The particle sizes are plotted in frequency (%),f,and cumulative % of undersize particles, u, versus particle diameter.

The expansion properties of the product particles were investigated intwo ways: tube expansion and observation with an optical microscopeusing a hot stage attachment.

In the tube expansion procedure, 0.20 g of the dried microsphere powderwas placed in a 10 mL graduated tube, which was then immersed and heatedin an 80° C. water bath. Instead of measuring the expansion ratio, themaximum expanded volume was used as the criteria of expansion.

The second method utilized the direct visual observation of particlesunder an optical microscope with a hot stage attachment that cangradually increase the temperature. By this means, the onset temperatureof expansion, T_(o.e.), termination temperature of expansion, T_(t.e.),and the onset temperature of shrinkage (loss of gas), T_(o.s.), wereobtained.

Several sets of screening examples were designed and carried out. Thedesign used here was based on Plackett-Burman's basic designs for 8, 12,16, 20, or up to 100 experiments. In each of these, N−1 factors can bestudied. In general, one determines how many variables need to beincluded and then one chooses the design that most nearly satisfies thatnumber. Any factors not assigned can be listed as dummies.

For a certain variable A in an eight experiment design, its effect onthe response (E_(A)) is simply the difference between the average valueof the response for the 4 runs at high level (R(+)) and the averagevalue of the response for the 4 runs at low level, (R(−)), asillustrated:

$\begin{matrix}{E_{A} = {\frac{R( + )}{4} - \frac{R( - )}{4}}} & {{Equation}\mspace{11mu}(3)}\end{matrix}$Dummy variables can be used to estimate the variance of an effect(V_(eff)), say:

$\begin{matrix}{V_{eff} = \frac{\sum\left( E_{dummy} \right)^{2}}{n}} & {{Equation}\mspace{14mu}(4)}\end{matrix}$where n is the number of dummy variables. Employing V_(eff) to calculatethe standard error of an effect (S.E_(eff)) by:

$\begin{matrix}{{S \cdot E_{eff}} = \sqrt{V_{eff}}} & {{Equation}\mspace{14mu}(5)}\end{matrix}$

The significance of each effect can be determined using a t-test

$\begin{matrix}{t = {\frac{effect}{s \cdot E_{eff}} = \frac{effect}{\sqrt{V_{eff}}}}} & {{Equation}\mspace{14mu}(6)}\end{matrix}$

Based on the Plackett-Burman basic design for 8 experiments, fivevariables and five responses in the first set of screening Examples werechosen as shown in Table 3.

TABLE 3 Screening Examples 18–29: Design and Results. Expd. PS PSD PSD/Vol. T_(o.e) T_(o.s.) Ex. Sample A B C D E (F) (G) (μm) (μm) PS (mL) (°C.) (° C.) 18 Y017 + + + − + − − 27.2 7.0 0.26 7.0 74 95 19 Y018 − + + +− + − 18.2 5.5 0.31 9.2 75 94 20 Y019 − − + + + − + 13.4 3.1 0.24 5.5 76103 21 Y020 + − − + + + − 12.2 3.9 0.32 0.8 74 98 22 Y021 − + − − + + +20.0 6.0 0.30 9.8 74 100 23 Y022 + − + − − + + 14.6 11.2 0.77 0.7 71 7824 Y023 + + − + − − + 26.7 7.1 0.27 6.6 69 94 25 Y024 − − − − − − − 14.03.5 0.25 7.8 74 103 26 Y017′ + + + − + − − 23.8 7.8 0.33 7.8 74 95 27Y018′ − + + + − + − 16.6 6.1 0.37 6.9 75 96 28 Y021′ − + − − + + + 17.57.3 0.42 9.5 74 102 29 Y022′ + − + − − + + 14.7 6.7 0.46 1.0 69 72 * A =level of alcohol (+) 3% wt (6 g) (−) 1% wt (2 g) based on water B = typeof alcohol (+) Methyl (−) Hexanol C = MW of PVAm (+) 250 K (−) 15 K D =agitation speed (+) 1960 rpm (−) 1500 rpm E = agitation time (+) 30 min(−) 10 min ** Variables (F) and (G) are dummies, which do not representany real parameter. *** Samples Y017′, Y018′ and Y021′, Y022′ used thesame recipes as Y017, Y018, Y021 and Y022, they were repeated becausethe latter ones had large tails in the particle size distribution. ****PS is mean particle size, PSD is standard deviation of sizedistribution, PSD/PS is relative deviation of size distribution.

The significance of the investigated variables, namely, level and typeof alcohol, molecular weight of PVAm, agitation speed and agitationtime, was calculated and is reflected in Table 4 and Table 5.

TABLE 4 Significance of Variables (t-value), based on Ex. 20, 21 and24–28 PS PSD Expd. Vol. T_(o.e.) T_(o.s.) Variable (μm) (μm) (mL) (° C.)(° C.) A 1.29 1.65 −3.59 −2.2 −1.70 B 3.23 0.58 3.72 −0.6 0.05 C 0.040.93 −0.54 1 −1.21 D −0.45 −1.2 −0.67 0.2 0.63 E −0.06 −1.08 −0.25 1.81.31 (F) −1.39 0.87 −1.34 0.2 −1.21 (G) 0.26 1.11 −0.46 −1.4 −0.73

TABLE 5 Significance of Variables (t-value), based on Examples 18–25 PSPSD Expd. Vol. T_(o.e.) T_(o.s.) Variable (μm) (μm) (mL) (° C.) (° C.) A1.26 1.85 −2.00 −2.03 −1.86 B 2.38 4.27 2.33 −0.16 0.45 C −0.16 0.88−0.52 0.47 −1.28 D −0.09 −1.69 −0.94 0.47 0.79 E −0.39 −0.66 0.19 1.721.36 (F) −1.34 1.10 −1.41 −0.16 −1.12 (G) 0.46 0.88 −0.10 −1.41 −0.87

From Tables 3,4 and 5, the following is observed:

(1) Adding methanol can effectively increase the particle size and valueof PSD. But if the value of PSD/PS (relative deviation of sizedistribution) is considered instead of PSD (standard deviation of sizedistribution) as the criteria of the distribution broadness, it isdiscovered that actually adding methanol can improve the uniformity ofthe particle size, which is consistent with the reported results.

(2) Methanol, which has higher solubility parameter, δ=14.5(cal/cm³)^(1/2), than hexanol does, δ=10.7 (cal/cm³)^(1/2), is a moreeffective additive in terms of increasing the size of the microspheres,and also results in a broader absolute but narrower relativedistribution, i.e. the average PSD/PS for the samples prepared usingmethanol is 0.320, whereas for the samples prepared using hexanol, it is0.406.

(3) Adding a suitable amount of alcohol can improve the extent ofexpansion due to the resulting larger particle size and narrower sizedistribution. As was observed, samples prepared with 2 g methanol hadthe largest expanded volume. However, the use of too much methanol inthis system may produce particles having a honeycomb structure, whereexpansion and loss of gas occurs in the same temperature range, 74 to 80° C., resulting in worse expansion.

(4) The higher agitation speed produced particles with a narrowerdistribution, since the significance of the agitation speed on theparticle size distribution is about −1.2˜−1.7. This may be attributed tothe narrower initial droplet size distribution obtained in theemulsification process. The agitation time has little, if any, effect onthe particle size, but it can improve the particle uniformity. However,it was surprising that agitation conditions did not affect the particlesize.

(5) The molecular weight of the PVAm is not a significant parameter forall responses because all the t-value of this variable are smallcompared to those of other variables. This independence of particle sizeon the molecular weight of the stabilizer is not consistent withequation (2), which predicts that the use of a higher molecular weightPVAm would result in larger particles.

Knowing that methanol can improve both the uniformity and the expansionproperties of the particles, and the solubility parameters of thealcohols is rather important, the following further examples reflect theinfluence of other types of alcohols.

U.S. Pat. No. 3,945,956 discloses that hydroxyl containing compoundsimprove both the morphology and expansion characteristics of theexpandable microspheres, such as particle size, size uniformity,temperature range of expansion and expandability. The applicablealcohols are represented as R-(OH)_(n), where R is an alkyl radicalcontaining from 1 to 6 carbon atoms and n is an integer from 1 to 4.

The definition of solubility parameter is given in the form:δ=C^(1/2)  Equation (7)C=[(ΔH−RT)/V _(m)]^(1/2)  Equation (8)where δ is the solubility parameter, C is the cohesive energy density,ΔH is the heat of vaporization, R is the gas constant, T is thetemperature, V_(m) is the molar volume of the solvent.

The solubility parameter can be estimated from a theoreticalcalculation:δ=(ρΣG)/M  Equation (9)where ρ is the solvent density, G is the group molar attractionconstants at 25° C., M is molecular weight of the solvent.

TABLE 6 Physical Properties of Normal Alcohols N ρ M δ δ(C_(n)H_(2n+2)O) (g/cm³) (g/mol.) (calculated) (CRC Handbook) 1 0.791 3210.87 14.5 2 0.794 46 9.89 10.0 3 0.804 60 9.46 10.5 4 0.810 74 9.1813.6 5 0.811 88 8.96 11.6 6 0.814 102 8.82 10.7

In order to examine the effect of the solubility parameters and higheramounts of alcohol, ethanol and 1-butanol were selected as the testedalcohols, and the level of the alcohols was increased in the followingExamples 27–34. Together with the alcohol, the effect of the amount ofLudox®, the ratio of PVAm/Ludox®, and NaCl was investigated . Theresults are collected in Table 7.

TABLE 7 Screening Examples 30–37 PS PSD Expd. T_(o.e) T_(o.s.) Ex.Sample A B C D E (F) (G) (μm) (μm) Vol (mL) (° C.) (° C.) 30 Y0252 + + +− + − − 15.7 5.5 1.1 72 74 31 Y0262 − + + + − + − * * * * * 32 Y0272 −− + + + − + * * * * * 33 Y0282 + − − + + + − 16.1 6.7 9.9 73 98 34 Y0292− + − − + + + 14.1 5.6 5.3 76 100  35 Y0302 + − + − − + + 11.8 4.4 0.674 78 36 Y0312 + + − + − − + 29.8 9.3 6.8 72 84 37 Y0322 − − − − − − −20.2 7.0 9.8 74 95 A = level of Ludox (+) 38 g (30 wt %) (−) 22 g (30%wt) B = ratio of silica to PVAm (+) 75 (−) 37.5 (standard ratio ofsilica/PVAm = 30 g × 30%/0.12 g = 75) C = type of alcohol (+) Butanol(−) Ethanol D = level of alcohol (+) 10 g (5%) (−) 6 g (3%) E = level ofsalt (+) 10 g (−) 4 g * Samples Y0262, Y0272 indicated as “*” wereExamples resulting in coagulation during polymerization and could notgive any response.

For this set of examples, the following was observed:

(1) Samples Y026 and Y027 coagulated during polymerization. Noting thatthey both have 10 g butanol in their system, it is believed thatbutanol, having a higher solubility parameter, may dramatically decreasethe interfacial tension and further destabilize the emulsion system.

(2) All samples containing butanol had poor expansion properties,observation under an optical microscope indicated that a large amount ofparticles did not contain isopentane droplets and could not expand;those particles containing isopentane could expand but also shrank below80° C.

(3) Adding ethanol can effectively increase the particle size andimprove the expansion.

Two additional Example sets reflected in Tables 8 and 9 varied,respectively: (1) lowering the high level of butanol from 5 wt. % to 4wt. % (8 g)(Examples 38–39); and (2) decreasing the amount of butanolfrom 5 wt. % to 1 wt. % and take 1 wt % as (+) (Examples 40–46). Example38 failed, when the stabilizer level was low (amount of Ludox®=22 g,silica/PVAm=75) in sample Y0263, since the system was not stable.

TABLE 8 PS PSD Expd. Vol. Ex. Sample A B C D E (F) (G) (μm) (μm) (mL)T_(o.e.) T_(o.s.) 1 Y0263 − + + + − + − * * * * * 2 Y0273 − − + + + − +12.5 4.8 0.5 * * (no exp)

In the second additional set, samples Y026 , Y027, Y028 and Y031 wereredone. There was no coagulation during any polymerization. Theresponses were measured and collected together with Y025, Y029, Y030,Y032 to make a whole group, as set forth in Screening Examples 40–47,shown in Table 9.

TABLE 9 Screening Examples 40–47 PS PSD PSD/ Expd. T_(o.e) T_(o.s.) Ex.Sample A B C D E (F) (G) (μm) (μm) PS Vol. (mL) (° C.) (° C.) 40Y025 + + + − + − − 15.7 5.5 0.35 1.1 72 74 41 Y026 − + + + − + − 11.64.3 0.37 7.7 72 98 42 Y027 − − + + + − + 11.9 4.6 0.39 7.6 73 98 43Y028 + − − + + + − 12.4 5.3 0.43 8.7 74 98 44 Y029 − + − − + + + 21.07.4 0.35 10.5 76 100 45 Y030 + − + − − + + 11.8 4.4 0.37 0.6 74 78 46Y031 + + − + − − + 16.7 5.5 0.33 9.5 74 100 47 Y032 − − − − − − − 20.27.0 0.35 9.8 74 95 A = level of Ludox (+) 38 g (30 wt %) (−) 22 g (30%wt) B = ratio of silica/PV Am (+) 75 (−) 37.5 C = type of alcohol (+)Butanol (−) Ethanol D = level of alcohol (+) 2 g (1%) (−) 6 g (3%) E =level of salt (+) 10 g (−) 4 g

TABLE 10 Significance (t-value) of Variables of Screening Examples 40–47PS PSD/ Expd. Variable (μm) PS Vol. (mL) T_(o.e.) T_(o.s.) A −1.46 0.27−21.6 −2.03 −1.86 B 1.573 −1.5 2.88 −0.16 0.45 C −3.48 0.28 −29.53 0.47−1.28 D −2.908 1.06 15.80 0.47 0.79 E 0.13 1.12 0.41 1.72 1.36 (F) −1.391.27 −0.69 −0.16 −1.12 (G) 0.27 −0.62 1.24 −1.41 −0.87

The results shown in Tables 9 and 10, reflect the following:

(1) The level of colloidal silica has little effect on the PSD/PS, butit can effectively influence the extent of expansion. A smaller amountof silica results in better expansion. Its effect on the particle sizewas not that significant, but higher amounts of silica would decreasethe particle size. This observation is consistent with the reportedresults of Kang, (Ming-Huang J. Kang, Ph.D. dissertation, LehighUniversity, 1986), which showed a decrease in particle size withincreased amount of colloidal silica.

(2) The Ludox®/PVAm ratio showed the combined effect of the amount ofcolloidal silica and PVAm. When the ratio was high (lower amount of PVAmfor a fixed amount of Ludox®, or a higher amount of Ludox® for a fixedamount of PVAm), the resulting microspheres had a larger particle size,narrower size distribution, and higher extent of expansion.

(3) The level of salt did not affect the particle size and expansionratio, but apparently broadened the particle size distribution andincreased the onset temperature of both expansion and shrinkage.

(4) Ethanol, with its lower solubility parameter, was helpful forproducing larger particles and better expansion, while butanol had theopposite effect. An increased amount of ethanol resulted in theformation of larger particles and had little effect on expansion withinthe range from 2 to 6 g alcohol. However, an increased amount of butanoldid not result in the formation of larger particles or improve theexpansion. This observation, i.e., that the alcohol with highersolubility parameter does not favor increasing particle size, itsdistribution and expansion, is the opposite of the results obtained fromthe comparison of methanol and hexanol.

Further Examples 48–53 reflect characteristics of the H₂O₂ treatmentusing an impeller to agitate the mixture at various agitation speeds.The Examples include two types of samples: dry particles afterfiltration and original slurry taken directly from the reactor. For dryparticles, 30 g dry particles were mixed with 45 g DI water and themixture was treated with 0.7 g 35% H₂O₂ solution at 50° C. for 3.5 hr.For original slurry, 75 g were taken for further treatment.

TABLE 11 Comparison of Expansion Behavior and the Appearance of HydrogenPeroxide Treated Particles for Various Treatment Conditions. Expd. Vol.Particle appearance Ex. Dispersion Mixing RPM (mL) T_(o.e.) and behavior48 V1500 Dry Impeller 1500 5.0 73 All transparent; 100% particlesexpanded 49 V600 Dry Impeller  600 5.0 72 All transparent; 100%particles expanded 50 V200 Dry Impeller  200 3.3 73 Most aretransparent; particles opaque microspheres cannot expand 51 VO1500Original Impeller 1500 4.0 73 Most are transparent; slurry opaquemicrospheres cannot expand 52 VT Dry B.P.* N/A 3.0 73 Most aretransparent particles 53 VOT Original B.P.* N/A 0.8 90 All are opaque;slurry No apparent expansion *bottle polymerization unit (30 rpm)

Table 11 reflects the following:

(1) The slurries made from dry particles resulted in better expansion,as shown by comparing VT/VOT and V1500/VO1500. This may be due to thepresence of ingredients in the original slurry, which can decompose thehydrogen peroxide.

(2) Treatment in a bottle polymerization unit is not as efficient asthat obtained by agitation with an impeller. If it is assumed that theend-over-end method of the bottle polymerization can give sufficientmixing, then the results show that shearing the dispersion is criticalto remove impediments to expand.

(3) A higher agitation speed (RPM) can result in better expansion. Thehigher RPM produces a larger shear force and better mixing.

(4) Though the mechanism of surface treatment is not known withcertainty, the hydrogen peroxide most likely removes the colloidalsilica sitting on the particle surface, which make the particles opaquebefore treatment and impede the particle expansion.

The above examples reflect that the type and level of alcohol, and theamount of PVAm effect the dispersion stability and microsphereproperties. Examples 54–69 as shown in Table 12 further demonstratethese effects. In Examples 54–69, the amount of Ludox® (35 wt % ofcolloidal silica) was held constant at 22 g, and the amount of NaCl wasmaintained at 4 g, Na₂Cr₂O₇ (wt 2.5%) was 3.40 g, and DI water was 200 gas well. The composition of the oil phase is the same as that found inthe standard recipe. The results are collected in Table 13.

It is clearly seen that an increase in the amount of ethanol willbroaden the absolute particle size distribution, but in terms of therelative distribution, this is not necessarily true. In spite of thecomplexity, in every four samples with the same amount of PVAm (e.g.CM01–CM04, PVAm=0.05 g) the microspheres with the narrowest relativedistribution always had the best expandability. This observationrevealed the relation between the size uniformity and the expandabilityof the microspheres. A relatively larger expanded volume would beobtained if the particle size were more uniform, due to the higherefficiency of packing. The examples prepared with more ethanol beganexpanding and shrinking at lower temperatures, which revealed that theethanol might not only decrease the interfacial tension of the dropletto make larger particles, but also change the composition of theparticle shell.

TABLE 12 Examples 54–69 Varying Ethanol and PVAm in the Aqueous PhaseExample 54 55 56 57 58 59 60 61 Sample CM01 CM02 CM03 CM04 CM05 CM06CM07 CM08 Ethanol(g) 1 3 5.5 8 1 3 5.5 8 PVAm(g) 0.05 0.05 0.05 0.050.10 0.10 0.10 0.10 Example 62 63 64 65 66 67 68 69 Sample CM09 CM10CM11 CM12 CM13 CM14 CM15 CM16 Ethanol(g) 1 3 5.5 8 1 3 5.5 8 PVAm(g)0.15 0.15 0.15 0.15 0.20 0.20 0.20 0.20

TABLE 13 Effect of Amount of Ethanol and PVAm Expd. PS PSD PSD/ Vol.T_(o.e.) T_(t.e.) T_(o.s.) T_(t.s.) Ex. Sample (μm) (μm) PS (mL) (° C.)(° C.) (° C.) (° C.) 54 CM01 14.8 5.37 0.363 3.0 77 96 102 106 55 CM0216.1 6.68 0.415 7.2 75 94 103 111 56 CM03 22.9 6.40 0.279 8.7 72 90 94104 57 CM04 47.2 21.8 0.462 2.0 68 80 83 94 58 CM05 14.8 5.36 0.362 6.575 94 106 113 59 CM06 16.8 6.77 0.403 8.4 75 94 104 109 60 CM07 21.27.34 0.346 10.5 72 75 96 105 61 CM08 31.0 15.0 0.484 5.4 67 72 86 93 62CM09 15.6 5.63 0.361 7.7 76 95 107 113 63 CM10 17.8 7.01 0.394 9.6 73 77104 109 64 CM11 20.9 6.91 0.331 10.6 71 75 96 105 65 CM12 24.3 8.770.361 9.3 68 73 90 100 66 CM13 13.8 5.12 0.371 8.7 75 77 103 116 67 CM1417.3 6.41 0.371 10.9 73 76 100 110 68 CM15 22.1 6.04 0.273 11.0 69 74 95116 69 CM16 22.4 5.98 0.267 10.2 69 74 94 125 * The expansion of themicrospheres was measured in graduated tubes at 80° C., the amount ofair dried microspheres was 0.2 g, and the maximum expanded volume of themicrospheres (Expd. Vol.) was used to define the expandability of themicrospheres. ** T_(o.e.) = onset temperature of expansion T_(t.e.) =termination temperature of expansion T_(o.s.) = onset temperature ofshrinkage T_(t.s.) = termination temperature of shrinkage

At the highest alcohol level, the particles had a honeycomb structure,which contained smaller particles therein, (as shown in FIG. 6). Thehoneycomb structure is undesirable in this project due to the impairmentof the thermal expansion and mechanical properties. The particle sizeincreased with the amount of ethanol, and this effect was weakened whenthe level of PVAm in the system was high, as shown in FIG. 1. This isconsistent with the former observations that an increased PVAm amountresults in the formation of smaller particles with narrowerdistributions. PVA_(m) acted similarly to a surfactant, which canstabilize the smaller droplets.

In order to find an actual recipe for microspheres having a desiredparticle size and expansion properties, (i.e. expanding within a narrowrange of temperatures, excellent expandability, and holding gas at hightemperature), a contour plotting technique can be used to analyze thepartitioning in 3-D space with respect to the amount of PVAm andethanol. By using this technique, linear extrapolation is used betweenexperimental points to obtain intermediate values, and those similarvalues can be connected to yield isocontour lines.

FIG. 2 shows that, compared to ethanol, the amount of PVAm is not themost important parameter to control the particle size, but when thelevel of ethanol is high, suitable amounts of PVAm can be added toweaken its influence.

The contour plot in FIG. 3 shows the expanded volume of the particleswith respect to the amount of PVAm and ethanol. FIG. 3 shows that theamount of ethanol and PVAm had a combined effect on the expansion.Adjustment of both parameters achieves the maximum expansion at anoptimum point or, most likely, an optimum region. Points yielding thesame expanded volumes that were 5, 8 and 10 mL respectively, were foundand connected to obtain three isotherms. An increase in the amount ofPVAm improves the expandability of the microspheres, but when the amountof ethanol is increased, the expanded volume first increases to achievea maximum with a medium amount of ethanol, and then decreases.

The expansion process was recorded under a microscope with a hot stageattachment and photographed. The visual observation of the microspheresheated by the hot stage revealed that the particle expansion had fivestages:

(1) The microspheres held their shape and did not expand beforeT_(o.e.).

(2) When the temperature approached T_(o.e), the isopentane corevaporized and expanded the shell. Generally the larger spheres beganexpansion earlier than the smaller one. Sometimes some particles couldhold their shape up to 85° C. However, it is desirable that theparticles complete expansion over a narrow range of temperature.

(3) After the expansion was completed, the particles would maintaintheir shape until T_(o.s.). It is desirable that the particles have ahigh T_(o.s.).

(4) The particles begin losing gas when reaching T_(o.s.). Some becomesmaller gradually and some break abruptly like balloons.

(5) If the temperature is increased further, the particles lose alltheir gas and melt.

FIGS. 4 and 5 show the particles from Example 54, sample CM01 (Expd.Vol.=3.0 mL) before and after expansion, it was found that the particlesize was relatively small, (i.e. d=10 μm) and upon heating someparticles did not expand (black particles).

FIGS. 6 and 7 are for the particles from Example 57, sample CM04 (Expd.Vol.=2.0 mL), which had highest amount of ethanol and lowest level ofPVAm. A so-called honeycomb structure was found in these large particles(d=48 μm). These microspheres began expansion at a lower temperature,and due to the fast shrinkage after expansion, they did not result in asatisfactory expansion at 80° C.

The images of microspheres from Example 68, sample CM15 are shown inFIGS. 8 and 9, which clearly show that the size of these microspheres isintermediate, around 20 μm and more uniform. We could also see theliquid droplets through the transparent particle shells. These particlescould totally expand and resulted in excellent expansion.

EXAMPLES 18–69 reflect that the composition of the aqueous phase has agreat effect on the morphology and expansion properties of themicrospheres. The amount and type of alcohol used in the suspensionpolymerization recipe had the most significant effect. Methanol, andethanol increased the particle size and narrowed the particle sizedistribution. A suitable amount of methanol or ethanol brings about asharp expansion of the particles during heating resulting from theuniformity of the particle properties. However, too much methanol orethanol will produce particles with a honeycomb structure, which do notmaintain the particle integrity at higher temperatures, and lead to apoor expansion. The use of butanol did not improve the thermal-expansionproperties. The use of higher amounts of poly(vinyl amine) (PVAm), whichacted as a steric stabilizer together with the colloidal silica,produced microspheres that were smaller and more uniform in size.However, the molecular weight of poly(vinyl amine) did not affect theparticle properties. The amount of Ludox® colloidal silica had littleeffect on the particle size and size distribution, but it did affect thedegree of expansion of the particles. Smaller amounts of Ludox® resultedin better expansion. The level of salt did not have any effect on theparticle size, but it did broaden the particle size distribution andincreased the onset temperature of both expansion and shrinkage.

A higher agitation speed during the preparation of the suspensionproduced particles with a narrower size distribution. This may beattributed to the narrower initial droplet size distribution obtained inthe emulsification process. The agitation time had little effect on theparticle size, but it appeared to narrow the particle size distribution.

The presence of shear during H₂O₂ surface treatment enhanced theexpansion properties of the particles. Air-dried particles had a betterexpansion after H₂O₂ surface treatment compared to the original slurrytaken directly from the reactor.

Foam Including Polymeric Microspheres

Foams in accordance with the present invention are preferablymanufactured using an extruder, such as the extruder system 102schematically illustrated in FIG. 10. Use of the extruder provides thebest results, but other conventional mixing methods may be used.

The extrusion system 102 includes a single or twin screw extruder 104and an associated reservoir system 106. The extruder 104 includes aseries of barrels C1–C12 and an extruder head 120. Preferably a twinscrew extruder is employed such as described in U.S. Pat. No. 5,723,506.

The reservoir system 106 includes a plurality of reservoirs 150–156 fromwhich the foam components are supplied. The reservoirs 150–156 feed thefoam component materials to the barrels C1–C12 and head 120 of theextruder 104 via a network of feed lines and valves as illustrated.

In manufacturing foam using the extrusion system of FIG. 10, polymericmicrospheres are preferably provided to the extruder 104 at barrel C1from a fill station 150 using a side fill feeder which provides ametered flow of unexpanded microspheres to the screw of the extruder.Due to the light weight of the microspheres, using a gravity feed can beproblematic so a side fill feeder is preferred. Additional microspheresare preferably provided to the extruder 104 at barrel C4 from a fillstation 152 . Overall, at least 10% by weight, normally more than 25% byweight, of the expandable microspheres which encapsulate anon-halogenated hydrocarbon chemical or a non-halogenated hydrocarbonchemical blend as a primary blowing agent are preferably added.

For best results, it is preferred to use two different average sizes ofmicrospheres when making boardstock or bunstock foam to enhancestructural rigidity and strength. The larger size microspheres arepreferably introduced first at barrel C1 and the relatively smallermicrospheres are preferably introduced at barrel C4.

Preferably, the total microsphere component of the foam is 50% of thelarger microspheres and 50% of the smaller microspheres by weight. Thisrange may be varied from 30/70 to 70/30 so that at least 30% of themicrospheres have a relatively small average unexpanded diameter with astandard deviation less than 3 microns and at least 30% of themicrospheres have a relatively large average unexpanded diameter with astandard deviation less than 9 microns. The unexpanded diameter of thelarger microspheres is preferably at between 10 and 200 microns leastand is 1.5 times greater than the unexpanded diameter of the smallermicrospheres. The foam may have at least 45% of the microspheres havingthe smaller average unexpanded diameter with a standard deviation lessthan 2 microns and at least 45% of the microspheres having the largeraverage unexpanded diameter with a standard deviation less than 8microns where the larger diameter is between 10 and 100 microns and isat least two times greater than the smaller diameter. Microsphereshaving a heat activatible crosslinking agent and/or a surfacefunctionalization agent are preferred, particularly those receiving ahydrogen peroxide treatment to remove silica on the polymer shells.

In one example, the smaller microspheres had an average unexpandeddiameter of between 6–7 microns with a standard deviation less than 2microns and the larger microspheres had an average unexpanded diameterof 14 microns with a standard deviation less than 3 microns. In anotherexample, the smaller microspheres had an average unexpanded diameter ofbetween 6–7 microns with a standard deviation less than 2 microns andthe larger microspheres had an average unexpanded diameter of 19 micronswith a standard deviation less than 3 microns.

Isocyanate solution is preferably mixed and fed to barrels C2 and C6 ofthe extruder 104 from reservoirs 151 and 153 . The isocyanate solutionmay be optionally pre-mixed with a dispersing agent and/or surfactant atreservoirs 151 and 153 and provided to the extruder 104 with theisocyanate at barrels C2 and C6.

Polyol is preferably provided from a reservoir 155 and fed to theextruder 104 at barrel C9. Surfactant, curing agent and foaming agent ispreferably pre-mixed with the polyol contained in the reservoir 155 andfed to the extruder 104 at barrel C9.

The primary blowing agent is encapsulated within the microspheres. Assuch, the microspheres themselves function as a blowing agent as theyexpand during the foam making process. However, additional,non-encapsulated foaming or blowing agents can be used, preferably nomore than 2% by weight as reflected in the preferred formulations, FIGS.12 and 13. More preferably, less than 1% by weight of non-encapsulatedblowing agent is used in the manufacture of the inventive foam. Thepreference for little or no non-encapsulated blowing agent readilypermits the use of highly flammable non-halogenated hydrocarbons withoutthe need to take extra explosive proofing precautions for themanufacturing site. However, using the microspheres functionally as ablowing agent is advantageous even if the microspheres are not theprimary blowing agent.

When used, supplemental foaming and/or blowing agents are preferablyprovided from a reservoir 154 and fed to the extruder 104 at barrel C8without previous mixing with other components. Additionally,supplemental foaming and/or blowing agents may be mixed with the polyolat reservoir 155 prior to entry to the extruder 104 at barrel C9. Forexample, foaming agent is provided to extruder 104 at barrel C9 afterthe foaming agent is first mixed with a polyol/surfactant mixture.

Fire retardants such as polymeric phosphate and brominated-ester arepreferably pre-mixed with the polyol at reservoir 155 prior to entry tothe extruder 104 at barrel C9.

Catalyst is preferably introduced into the extruder 104 via an extruderhead 120 from reservoir 156. A cross-sectional side view of the extruderhead 120 of the extrusion system is shown in FIG. 11.

In making foam, the mixture of the component parts of the unexpandedpolymeric microspheres, isocyanate, polyol, and additional materials,without the catalyst, arrives via a hose 200 (shown in FIG. 10) to anentry port 202 in a mixing block 204 of the extruder head 120. At mixingblock 204, the component mixture travels via a worm gear 206 to agitator208 located in a cavity area 210. Concurrently, catalyst enters at acatalyst port 214 and travels along a duct 215 to arrive in the cavityarea 210 via a catalyst entry port 216. The mixture of the componentparts of the expandable microspheres, isocyanate, polyol and additionalagents and catalyst are mixed together by agitator 208 in the cavityarea 210 and continues out of the cavity area 210, preferably onto aconveyor system such as the conveyor illustrated in U.S. Pat. No.5,723,506. Preferably, the cavity 210 is 2 to 3 inches wide and theagitator is rotated at approximately 3500 to 5500 rpm.

The conveyor may optionally apply facer material to one or both sides ofthe foam. As the extruded mixture is deposited on the conveyor, the heatof the reaction causes the microspheres to expand. Additional heat canbe applied by the conventional type of conveyor system which transportsthe foam through a heated chamber for curing.

A preferred method of manufacturing foam using the extruder of FIG. 10includes feeding relatively large polymeric microspheres from source 150to the extruder 104 at barrel C1. A mixture of isocyanate, dispersingagent and surfactant is fed to the extruder 104 at barrel C2 fromreservoir 151. Additional microspheres, preferably of a smaller averagediameter, which may optionally be mixed with graphite particles and/orcarbon-black, are added from source 152 and fed to the extruder 104 atbarrel C4. An additional mixture of isocyanate, dispersing agent andsurfactant is then added to the extruder 104 at barrel C6 from reservoir153. Blowing agent is provided to the extruder 104 at barrel C8 fromreservoir 154. Polyol, foaming and blowing agent, surfactant and curingagent are fed to the extruder 104 at barrel C9 from reservoir 155.Finally, a catalyst or catalyst mixture is provided to the extruder head120 from reservoir 156.

The production of foams based on isocyanates is known per se and isdescribed, for example, in German Offenlegungsschriften 1,694,142,1,694,215 and 1,720,768, as well as in Kunststoff-Handbuch [PlasticsHandbook], Volume VII, Polyurethane, edited by Vieweg and Hochtlen, CarlHanser Verlag, Munich 1966, and in the new edition of this tome, editedby G. Oertel, Carl Hanser Vedag, Munich, Vienna, 1983.

These foams are mainly those that comprise urethane and/or isocyanurateand/or allophanate and/or uretdione and/or urea and/or carbodiimidegroups. Preferred starting components include aliphatic, cycloaliphatic,araliphatic, aromatic and heterocyclic polyisocyanates, such as thosedescribed, for example, by W. Siefken in Justus Liebigs Annalen derChemie, 562, pp. 75–136, for example, those of the formulaQ(NCO)_(n)in which n denotes 2–4, preferably 2–3, and Q denotes an aliphatichydrocarbon radical of 2–18, preferably 6–10 carbon atoms, acycloaliphatic hydrocarbon radical of 4–15, preferably 5–10 carbonatoms, an aromatic hydrocarbon radical of 6–15, preferably 6–13 carbonatoms or an araliphatic hydrocarbon radical of 8–15, preferably 8–13carbon atoms, for example, such polyisocyanates as described in DE-OS2,832,253, pp. 10–11.

Particularly preferred are usually those polyisocyanates which aretechnically readily accessible, for example, the 2,4- and 2,6-toluylenediisocyanate as well as any mixture of these isomers (“TDI”);polyphenyl5 polymethylenepolyisocyanates, such as those obtained by ananiline formaldehyde condensation and subsequent treatment with phosgene(“crude MDI”), and polyisocyanates comprising carbodjimide groups,urethane groups, allophanate groups, isocyanurate groups, urea groups orbiuret groups (“modified polyisocyanates”), especially those modifiedpolyisocyanates which are derived from 2,4- and/or 2,6-toluylenediisocyanate and from 4,4′- and/or 2,4′-diphenylmethane diisocyanate.

The starting components may further be compounds of a molecular weightusually of 400 to 10,000, containing at least two hydrogen atomsreactive toward isocyanates. These comprise, besides compoundscontaining amino, thio, or carboxyl groups, preferably compoundscontaining hydroxyl groups, in particular compounds containing 2 to 8hydroxyl groups, especially those of a molecular weight of 1,000 to6,000, preferably 2,000 to 6,000, for example polyethers and polyestersas well as polycarbonates and polyester amides containing at least 2,usually 2 to 8, preferably 2 to 6 hydroxyl groups; these compounds areknown per se for the preparation of homogenous and cellularpolyurethanes and are disclosed, for example in DE-OS 2,832,253, pp.11–18.

When appropriate, compounds comprising at least two hydrogen atomsreactive toward isocyanates and of a molecular weight of 32 to 399 maybe used as further starting components. Also, in this case, compoundscontaining hydroxyl groups and/or amino groups and/or thiol groupsand/or carboxyl groups, preferably compounds containing hydroxyl groupsand/or amino groups, are understood to be those which are used as chainlengtheners or crosslinking agents. These compounds usually have 2 to 8,preferably 2 to 4 hydrogen atoms reactive toward isocyanates.Appropriate examples are disclosed in DE-OS 2,832,253, pp. 19–20. Otherexamples of polyisocyanates and polyols useful in the invention aredescribed in U.S. Pat. No. 5,149,722, co-owned by the assignee of thepresent invention and incorporated herein by reference as if fully setforth.

Blowing agents which may be used to make foam include water and/orreadily volatile inorganic or organic substances and other auxiliaryvolatile blowing agents typically used to blow PUR/PIR foams. Water,however, used in small quantities serves as a foaming agent where otherblowing agents are used.

Organic blowing agents include acetone, ethylacetate;halogen-substituted alkanes, such as methylene chloride, chloroform,ethylidene chloride, vinylidene chloride, monofluoro trichloromethane,chlorodifluoromethane, dichlorodifluoromethane, dichlorodifluoroethane,dichlorotrifluoroethane; also halogenated and non-balogenatedhydrocarbon blowing agents.

Specific examples of non-halogenated hydrocarbon blowing agents include:pentane, butane, hexane, heptane, diethyl ether, isopentane, n-pentaneand cyclopentane.

Specific examples of halogenated hydrocarbon blowing agents include:1,1,1,4,4,4-hexafluorobutane (HFC-356); 1,1-dichloro-1 fluoroethane(HFC-141/b); the tetrafluoroethanes such as 1,1,1,2-tetrafluoroethane(HFC-134a); the pentafluoropropanes such as 1,1,2,2,3 pentafluoropropane(HFC-245ca), 1,1,2,3,3-pentafluoropropane (HFC 245ea),1,1,1,2,3-pentafluoropropane (HFC-245eb), and 1,1,1,3,3pentafluoropropane (HFC-245fa); the hexafluoropropanes such as1,1,2,2,3,3-hexafluoropropane (HFC-236ca), 1,1,1,2,2,3-hexafluoropropane (HFC-236cb), 1,1,1,2,3,3-hexafluoro-propane (HFC-236ea),1,1,1,3,3,3-hexafluoropropane (HFC-236fa); the pentafluorobutanes suchas 1,1,1,3,3-pentafluorobutane (HFC-365); and difluoroethanes such as1,1-difluoroethane (HFC-152a).

Inorganic blowing agents are, for example, air, CO₂ or N₂O. A blowingeffect may also be obtained by adding compounds which decompose attemperatures above room temperature giving off gases, such asazodicarbonamide or azoisobutyronitrile. Other examples of blowingagents may be found in Kunststoff-Handbuch, Vol. VII, by Vieweg andHochtlen, Carl-Hanser Verlag, Munich, 1966, on pages 108 and 109, 453 to455 and 507 to 510.

Different types of blowing agents are used in combination, but use of anon-halogenated hydrocarbon chemical as the primary blowing agent hasgenerally been avoided due to the flammability of foams whichconventionally result. Use of expandable microspheres as taught by thepresent invention permits the use of a non-halogenated primary blowingagent in an encapsulated form thereby making the production of foam withsuch material less hazardous.

When appropriate, other auxiliary agents and additives may be used atthe same time, such as:

-   water and/or other highly volatile organic substances as    propellants, i.e. foaming agents;-   additional catalysts of the type known per se in amounts up to 10%    by weight of the polyol component;-   surface-active additives, such as emulsifiers and foam stabilizers,    and-   reaction retardants, for example acidic substances such as    hydrochloric acid or organic acid halides, also cell regulators of    the type known per se, such as paraffins or fatty alcohols or    dimethylpolysiloxanes, as well as, pigments or dyes and other flame    retardants of the type known per se, for example tricresyl    phosphate, also stabilizers against the effect of aging and    weathering, plasticizers and fungistats and bacteriostats as well as    fillers such as barium sulphate, kieselguhr, carbon black, or    whiting.

Other examples of surface active additives, foam stabilizers, cellregulators, reaction retardants, stabilizers, flame retardants,plasticizers, dyes, fillers, fungistats, bacteriostats to be used at thesame time if appropriate, as well as details concerning the use andaction of these additives are described in Kunststoff-Handbuch [PlasticsHandbook], Volume VII, edited by Vieweg and Hochtlen, Carl HanserVerlag, Munich 1966, for example on pages 103–113.

In accordance with the experimentation and testing performed by thepresent inventors, preferred formulations for the manufacturer ofPUR/PIR boardstock and bunstock are set forth in FIGS. 12 and 13,respectively. While preferred types and/or sources of the componentmaterials are identified, these are non-limiting examples. Various otheradditive materials as discussed above, preferably not exceeding 100parts by weight, may be added to the formulations set forth in FIGS. 12and 13.

Formulations for additional examples of preferred microspheres for foammanufacture are set forth in conjunction with FIGS. 14–16. In theseexamples a functional monomer is used in the oil phase to functionalizethe surface of the microsphere in order to promote network crosslinkingwithin the foam. This results in an anchoring effect of the unexpandedmicrospheres within the foam during the foam manufacturing process whichenhances foam formation and structural integrity of the final foamproduct which results after the microspheres have expanded.

Preferred functional monomers include glycidyl methacrylate,hydroxyethyl methacrylate, hydroxylpropyl acrylate and hydroxylpropylmethacrylate. These create alcohol functionalities on the microspheresurfaces which are reactive with isocyanates. Glycidyl methacrylate isalso capable of surface hydrolysis

Alcohol is introduced to the aqueous phase in addition to the use ofsalt, sodium chloride. The alcohol is preferably ethylene glycol.

EXAMPLE 70

The general method of microsphere synthesis follows the proceduresoutlined in Example 10 with the aqueous phase having the components setforth in FIG. 14 and the oil phase having the components set forth inFIG. 15. In this case glycidyl methacrylate serves as the networkcrosslinking agent.

EXAMPLE 71

The general method of microsphere synthesis follows the proceduresoutlined in Example 10 with the aqueous phase having the components setforth in FIG. 14 and the oil phase having the components set forth inFIG. 16. In this case hydroxylpropyl methacrylate serves as the networkcrosslinking agent.

1. A polyurethane and/or polyisocyanurate rigid insulation foam madeusing expandable microspheres which encapsulate a primary blowing agentsuch that the microspheres are expanded during foam making to functionas a blowing agent by mixing: 160 to 310 PBW expandable microsphereshaving an encapsultated blowing agent and an average unexpanded diameterless than 50 microns; 191 to 500 PBW isocyanate; 75 to 125 PBW polyol;and 14 to 201 PBW other ingredients with less than 2% by weight ofnon-encapsulated blowing agents.
 2. The foam according to claim 1wherein the encapsulated blowing agent is selected from the groupconsisting of pentane, butane, hexane, heptane, diethyl ether,isopentane, n-pentane and cyclopentane or blends of chemicals from saidgroup.
 3. Boardstock made of a rigid polyurethane and/orpolyisocyanurate foam made according to claim 1 by mixing: 160 to 310PBW expandable microspheres having an encapsultated blowing agent and anaverage unexpanded diameter less than 50 microns; 191 to 400 PBWisocyanate; 75 to 125 PBW polyol; and 14 to 188 PBW other ingredientswith less than 2% by weight of non-encapsulated blowing agents. 4.Bunstock made of a rigid polyurethane and/or polyisocyanurate foam madeaccording to claim 1 by mixing: 160 to 310 PBW expandable microsphereshaving an encapsulated blowing agent and an average unexpanded diametersize less than 50 microns; 192 to 500 PBW isocyanate; 75 to 125 PBWpolyol; and 14 to 201 PBW other ingredients with less than 2% by weightof non-encapsulated blowing agents.
 5. The foam according to claim 1made using at least 10% by weight expandable microspheres whichencapsulate a non-halogenated hydrocarbon chemical or a non-halogenatedhydrocarbon chemical blend as a primary blowing agent.
 6. The foamaccording to claim 5 wherein at least 30% of the microspheres have afirst average unexpanded diameter with a standard deviation less than 3microns and at least 30% of the microspheres have a second averageunexpanded diameter with a standard deviation less than 9 microns, saidsecond diameter is at least 1.5 times greater than said first diameterand is between 10 and 200 microns.
 7. The foam according to claim 6wherein at least 45% of the microspheres have said first averageunexpanded diameter with a standard deviation less than 2 microns and atleast 45% of the microspheres have said second average unexpandeddiameter with a standard deviation less than 8 microns and said seconddiameter is at least two times greater than said first diameter and isbetween 10 and 100 microns.
 8. A polyurethane and/or polyisocyanuraterigid insulation foam made using at least 10% by weight expandablemicrospheres which encapsulate a non-halogenated hydrocarbon chemical ora non-halogenated hydrocarbon chemical blend as a primary blowing agentby mixing: 160 to 310 PBW expandable microspheres having anencapsultated blowing agent and an average unexpanded diameter less than50 microns; 191 to 500 PBW isocyanate; 75 to 125 PBW polyol; and 14 to201 PBW other ingredients with less than 2% by weight ofnon-encapsulated blowing agents.
 9. The foam according to claim 8 madeusing at least 25% by weight expandable microspheres which encapsulate anon-halogenated hydrocarbon chemical or a non-halogenated hydrocarbonchemical blend as a primary blowing agent and less than 2% by weight ofany non-encapsulated blowing agents.
 10. The foam according to claim 8wherein the encapsulated blowing agent is selected from the groupconsisting of pentane, butane, hexane, heptane, diethyl ether,isopentane, n-pentane and cyclopentane or blends of chemicals from saidgroup.
 11. Boardstock made of a rigid polyurethane and/orpolyisocyanurate foam made according to claim 8 by mixing: 160 to 310PBW expandable microspheres having an encapsultated blowing agent and anaverage unexpanded diameter less than 50 microns; 191 to 400 PBWisocyanate; 75 to 125 PBW polyol; and 14 to 188 PBW other ingredientswith less than 2% by weight of non-encapsulated blowing agents. 12.Bunstock made of a rigid polyurethane and/or polyisocyanurate foam madeaccording to claim 8 by mixing: 160 to 310 PBW expandable microsphereshaving an encapsulated blowing agent and an average unexpanded diametersize less than 50 microns; 192 to 500 PBW isocyanate; 75 to 125 PBWpolyol; and 14 to 201 PBW other ingredients with less than 2% by weightof non-encapsulated blowing agents.
 13. The foam according to claim 8wherein at least 30% of the microspheres have a first average unexpandeddiameter with a standard deviation less than 3 microns and at least 30%of the microspheres have a second average unexpanded diameter with astandard deviation less than 9 microns, said second diameter is at least1.5 times greater than said first diameter and is between 10 and 200microns.
 14. The foam according to claim 10 wherein at least 45% of themicrospheres have said first average unexpanded diameter with a standarddeviation less than 2 microns and at least 45% of the microspheres havesaid second average unexpanded diameter with a standard deviation lessthan 8 microns and said second diameter is at least two times greaterthan said first diameter and is between 10 and 100 microns.
 15. Apolyurethane and/or polyisocyanurate rigid insulation foam made usingexpandable microspheres which encapsulate a blowing agent whichmicrospheres are expanded in the resultant foam, by mixing: 160 to 310PBW expandable microspheres having an encapsultated blowing agent and anaverage unexpanded diameter less than 50 microns; 191 to 500 PBWisocyanate; 75 to 125 PBW polyol; and 14 to 201 PBW other ingredientswith less than 2% by weight of non-encapsulated blowing agents; whereinat least 30% of the microspheres have a first average unexpandeddiameter with a standard deviation less than 3 microns and at least 30%of the microspheres have a second average unexpanded diameter with astandarddeviation less than 9 microns, said second diameter is at least1.5 times greater than said first diameter and is between 10 and 200microns.
 16. The foam according to claim 15 wherein at least 45% of themicrospheres have said first average unexpanded diameter with a standarddeviation less than 2 microns and at least 45% of the microspheres havesaid second average unexpanded diameter with a standard deviation lessthan 8 microns and said second diameter is at least two times greaterthan said first diameter and is between 10 and 100 microns.
 17. The foamaccording to claim 15 wherein the encapsulated blowing agent is selectedfrom the group consisting of pentane, butane, hexane, heptane, diethylether, isopentane, n-pentane and cyclopentane or blends of chemicalsfrom said group.
 18. Boardstock made of a rigid polyurethane and/orpolyisocyanurate foam made according to claim 15 by mixing: 160 to 310PBW expandable microspheres having an encapsultated blowing agent and anaverage unexpanded diameter less than 50 microns; 191 to 400 PBWisocyanate; 75 to 125 PBW polyol; 14 to 188 PBW other ingredients withless than 2% by weight of non-encapsulated blowing agents.
 19. Bunstockmade of a rigid polyurethane and/or polyisocyanurate foam made accordingto claim 15 by mixing: 160 to 310 PBW expandable microspheres having anencapsulated blowing agent and an average unexpanded diameter size lessthan 50 microns; 192 to 500 PBW isocyanate; 75 to 125 PBW polyol; 14 to201 PBW other ingredients with less than 2% by weight ofnon-encapsulated blowing agents.
 20. A method for the manufacture ofpolyurethane and/or polyisocyanurate rigid insulation foam comprising:introducing 160 to 310 PBW expandable microspheres having anencapsultated blowing agent and an average unexpanded diameter less than50 microns to the screw of an extruder; introducing 191 to 500 PBW of aisocyanate to the screw of the extruder; introducing 75 to 125 PBW of apolyol to the screw of the extruder; introducing 10 to 201 PBW otheringredients with less than 2% by weight of non-encapsulated blowingagents to the screw of the extruder; using the screw of the extruder tomix the expandable microspheres, isocyanate, polyol and otheringredients to and extruding the mixed ingredients in conjunction withmixing 1 to 12 PBW catalyst; and expanding the microspheres in theextruded mixture to produce rigid foam.
 21. The method according toclaim 20 used to make boardstock wherein: 191 to 400 PBW of saidisocyanate is introduced to the screw of the extruder; and 10 to 188 PBWsaid other ingredients with less than 2% by weight of non-encapsulatedblowing agents are introduced to the screw of the extruder of which 10to 50 PBW are fire retardants and 1 to 4 parts is a surfactant toproduce rigid foam boardstock.
 22. The method according to claim 20 usedto make bunstock wherein: 192 to 500 PBW said isocyanate to isintroduced to the screw of the extruder; and 10 to 201 PBW said otheringredients with less than 2% by weight of non-encapsulated blowingagents are introduced to the screw of the extruder of which 10 to 85 PBWare fire retardants, 1 to 5 parts is a dispersing agent and 1 to 5 partsis a surfactant to produce rigid foam bunstock.
 23. The method accordingto claim 20 further comprising extruding the mixture onto a conveyorsystem and applying facer material to one or more sides of the foamwhich is produced.
 24. The method according to claim 20 furthercomprising extruding the mixture onto a conveyor system and transportingthe foam through a heated chamber for curing whereby the microspheresexpand and maintain their expanded size and shape in the foam which isproduced.
 25. The method according to claim 20 wherein at least 30% ofthe microspheres have a first average unexpanded diameter with astandard deviation less than 3 microns and at least 30% of themicrospheres have a second average unexpanded diameter with a standarddeviation less than 9 microns, said second diameter is at least 1.5times greater than said first diameter and is between 10 and 200microns.